Low Noise

The ultimate aspiration of any detection method is to achieve such a level of sensitivity that individual quanta of a measured value can be resolved. In the case of chemical sensors, the quantum is one atom or molecule. Such resolution has so far been beyond the reach of any detection technique, including solid-state gas sensors hailed for their exceptional sensitivity [1-4]. The fundamental reason limiting the resolution of such sensors is fluctuations due to thermal motion of charges and defects [5] which lead to intrinsic noise exceeding the sought-after signal from individual molecules, usually by many orders of magnitude. Here we show that micrometre-size sensors made from graphene are capable of detecting individual events when a gas molecule attaches to or detaches from graphene's surface. The adsorbed molecules change the local carrier concentration in graphene one by one electron, which leads to step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material electronically, which makes it a promising candidate not only for chemical detectors but also for other applications where local probes sensitive to external charge, magnetic field or mechanical strain are required.

Many of the classification algorithms developed in the machine learning literature, including the support vector machine and boosting, can be viewed as minimum contrast methods that minimize a convex surrogate of the 0-1 loss function. The convexity makes these algorithms computationally efficient. The use of a surrogate, however, has statistical consequences that must be balanced against the computational virtues of convexity. To study these issues, we provide a general quantitative relationship between the risk as assessed using the 0-1 loss and the risk as assessed using any nonnegative surrogate loss function. We show that this relationship gives nontrivial upper bounds on excess risk under the weakest possible condition on the loss function: that it satisfy a pointwise form of Fisher consistency for classification. The relationship is based on a simple variational transformation of the loss function that is easy to compute in many applications. We also present a refined version of this result in the case of low noise, and we show that, in this case, strictly convex loss functions lead to faster rates of convergence of the risk than would be implied by standard uniform convergence arguments. Finally, we present applications of our results to the estimation of convergence rates in function classes that are scaled convex hulls of a finite-dimensional base class, with a variety of commonly used loss functions.

In current longitudinal magnetic recording media, high areal density and low noise are achieved by statistical averaging over several hundred weakly coupled ferromagnetic grains per bit cell. Continued scaling to smaller bit and grain sizes, however, may prompt spontaneous magnetization reversal processes when the stored energy per particle starts competing with thermal energy, thereby limiting the achievable areal density. Charap et al. have predicted this to occur at about 40 Gbits/in 2 : This paper discusses thermal effects in the framework of basic Arrhenius-Néel statistical switching models. It is emphasized that magnetization decay is intimately related to high-speedswitching phenomena. Thickness-, temperature-and bit-densitydependent recording experiments reveal the onset of thermal decay at "stability ratios" (KuV =kB T)0 = 35 6 2. The stability requirement is grain size dispersion dependent and shifts to about 60 for projected 40 Gbits/in 2 conditions and ten-year storage times. Higher anisotropy and coercivity media with reduced grain sizes are logical extensions of the current technology until write field limitations are reached. Future advancements will rely on deviations from traditional scaling. Squarer bits may reduce destabilizing stray fields inside the bit transitions. Perpendicular recording may shift the onset of thermal effects to higher bit densities. Enhanced signal processing may allow signal retrieval with fewer grains pers bit. Finally, single grain per bit recording may be envisioned in patterned media, with lithographically defined bits. Index Terms-Arrhenius-Néel model, dynamic coercivity, high K u alloys, magnetic recording, signal decay, thermal switching. I. INTRODUCTION A N overview of thermal effect limits in magnetic recording is presented. The emphasis is on continuous dimensional scaling of granular longitudinal recording media, where these effects will first become apparent. We try to answer the important question of how thermally stable today's media are and review the assumptions behind Charap's 40 Gbits/in limit prediction [1]. In particular, we discuss a new experimental approach to reliably determine media stability by combining long time signal decay measurements with short time write experiments. A brief outlook discusses materials alternatives, in particular high anisotropy media, and points to various options to avoid thermal effects. These include reduced bit aspect ratio recording, fewer grains per bit, perpendicular recording, possibly with thermal assist, and patterned media.

An applications-oriented review of optical parametric amplifiers in fiber communications is presented. The emphasis is on parametric amplifiers in general and single pumped parametric amplifiers in particular. While a theoretical framework based on highly efficient four-photon mixing is provided, the focus is on the intriguing applications enabled by the parametric gain, such as all-optical signal sampling, time-demultiplexing, pulse generation, and wavelength conversion. As these amplifiers offer high gain and low noise at arbitrary wavelengths with proper fiber design and pump wavelength allocation, they are also candidate enablers to increase overall wavelength-division-multiplexing system capacities similar to the more well-known Raman amplifiers. Similarities and distinctions between Raman and parametric amplifiers will also be addressed. Since the first fiber-based parametric amplifier experiments providing net continuous-wave gain in the for the optical fiber communication applications interesting 1.5-m region were only conducted about two years ago, there is reason to believe that substantial progress may be made in the future, perhaps involving "holey fibers" to further enhance the nonlinearity and thus the gain. This together with the emergence of practical and inexpensive high-power pump lasers may in many cases prove fiber-based parametric amplifiers to be a desired implementation in optical communication systems.

Abstrac/-SAR surveys from separate passes show relative shifts of the ground wavcnu m ber spectra thaI depend on the local slope and the off-nadir angle. We discuss the exploitation of this spectral sllift for different app] ications: I) generation of "low noise" intcrferograms benefiting phase unwrapping, 2) generation of quick-look interferograms, 3) decorrelation redllction by means of tunable SAl{ systems (TINSAR), 1 4) range resolution enhancement, and 5) the combination of SAR data gathered by different platforms (airborne and satell ite) for a "long-lime coherence" sludy.

A novel, fully 3D, high-resolution T 1 and T 2 relaxation time mapping method is presented. The method is based on steadystate imaging with T 1 and T 2 information derived from either spoiling or fully refocusing the transverse magnetization following each excitation pulse. T 1 is extracted from a pair of spoiled gradient recalled echo (SPGR) images acquired at optimized flip angles. This T 1 information is combined with two refocused steady-state free precession (SSFP) images to determine T 2 . T 1 and T 2 accuracy was evaluated against inversion recovery (IR) and spin-echo (SE) results, respectively. Error within the T 1 and T 2 maps, determined from both phantom and in vivo measurements, is approximately 7% for T 1 between 300 and 2000 ms and 7% for T 2 between 30 and 150 ms. The efficiency of the method, defined as the signal-to-noise ratio (SNR) of the final map per voxel volume per square root scan time, was evaluated against alternative mapping methods. With an efficiency of three times that of multipoint IR and three times that of multiecho SE, our combined approach represents the most efficient of those examined. Acquisition time for a whole brain T 1 map (25 ؋ 25 ؋ 10 cm) is less than 8 min with 1 mm 3 isotropic voxels. An additional 7 min is required for an identically sized T 2 map and postprocessing time is less than 1 min on a 1 GHz PIII PC. The method therefore permits real-time clinical acquisition and display of whole brain T 1 and T 2 maps for the first time. Magn Reson Med 49:515-526, 2003.

We demonstrate a frequency comb spanning an octave via the parametric process of cascaded four-wave mixing in a monolithic, high-Q silicon nitride microring resonator. The comb is generated from a single-frequency pump laser at 1562 nm and spans 128 THz with a spacing of 226 GHz, which can be tuned slightly with the pump power. In addition, we investigate the RF-noise characteristics of the parametric comb and find that the comb can operate in a low-noise state with a 30-dB reduction in noise as the pump frequency is tuned into the cavity resonance.

T-lymphocyte activation displays a remarkable combination of speed, sensitivity, and discrimination in response to peptide-major histocompatibility complex (pMHC) ligand engagement of clonally distributed antigen receptors (T cell receptors or TCRs). Even a few foreign pMHCs on the surface of an antigen-presenting cell trigger effective signaling within seconds, whereas 1 3 10 5 -1 3 10 6 self-pMHC ligands that may differ from the foreign stimulus by only a single amino acid fail to elicit this response. No existing model accounts for this nearly absolute distinction between closely related TCR ligands while also preserving the other canonical features of T-cell responses. Here we document the unexpected highly amplified and digital nature of extracellular signal-regulated kinase (ERK) activation in T cells. Based on this observation and evidence that competing positive-and negative-feedback loops contribute to TCR ligand discrimination, we constructed a new mathematical model of proximal TCR-dependent signaling. The model made clear that competition between a digital positive feedback based on ERK activity and an analog negative feedback involving SH2 domain-containing tyrosine phosphatase (SHP-1) was critical for defining a sharp liganddiscrimination threshold while preserving a rapid and sensitive response. Several nontrivial predictions of this model, including the notion that this threshold is highly sensitive to small changes in SHP-1 expression levels during cellular differentiation, were confirmed by experiment. These results combining computation and experiment reveal that ligand discrimination by T cells is controlled by the dynamics of competing feedback loops that regulate a high-gain digital amplifier, which is itself modulated during differentiation by alterations in the intracellular concentrations of key enzymes. The organization of the signaling network that we model here may be a prototypic solution to the problem of achieving ligand selectivity, low noise, and high sensitivity in biological responses. Citation: Altan-Bonnet G, Germain RN (2005) Modeling T cell antigen discrimination based on feedback control of digital ERK responses. PLoS Biol 3(11): e356.

Sixty-gigahertz power (PA) and low-noise (LNA) amplifiers have been implemented, based on algorithmic design methodologies for mm-wave CMOS amplifiers, in a 90-nm RF-CMOS process with thick 9-metal-layer Cu backend and transistor T MAX of 120 GHz/200 GHz. The PA, fabricated for the first time in CMOS at 60 GHz, operates from a 1.5-V supply with 5.2 dB power gain, a 3-dB bandwidth 13 GHz, a P 1dB of +6.4 dBm with 7% PAE and a saturated output power of +9.3 dBm at 60 GHz. The LNA represents the first 90-nm CMOS implementation at 60 GHz and demonstrates improvements in noise, gain and power dissipation compared to earlier 60-GHz LNAs in 160-GHz SiGe HBT and 0.13-m CMOS technologies. It features 14.6 dB gain, an IIP 3 of 6.8 dBm, and a noise figure lower than 5.5 dB, while drawing 16 mA from a 1.5-V supply. The use of spiral inductors for on-chip matching results in highly compact layouts, with the total PA and LNA die areas with pads measuring 0 35 0 43 mm 2 and 0 35 0 40 mm 2 , respectively. Index Terms-Characteristic current densities, CMOS millimeter-wave integrated circuits, MAX , T , inductors, low-noise amplifier (LNA), millimeter-wave, noise figure, power amplifier (PA), receiver, transformers, V-band, 60 GHz.

Th e generation of femtosecond optical pulses 1 has opened up a range of applications from real-time monitoring of chemical reactions through to ultrahigh-bit-rate optical communications 2 , and has led to new concepts in femtosecond optical networking, signal processing and transmission. In fact, lasers operating at multigigahertz repetition rates are now becoming key components for high-capacity telecommunication systems, photonic switching devices, optical interconnects, clocks for very-large-scale integrated microprocessors and high-speed electro-optic sampling systems.

We report on the design and fabrication of a new class of 50-nm self-aligned-gate pseudomorphic AlInAs / GaInAs High Electron Mobility Transistors (HEMT's) with potential for ultra-high-frequency and ultra-low-noise applications. These devices exhibit an extrinsic transconductance of 1740 mS / mm and an extrinsic current-gain cutoff frequency of 340 GHz at room temperature: the latter is the highest value yet reported for any three-thermal semiconductor device. We also report for the first time a detailed comparison of the smallsignal characteristics of a pseudomorphic and a lattice-matched AIInAs/GaInAs HEMT with similar gate length (50 nm) and gate-to-channel separation (17.5 nm): the former demonstrates a 16% higher transconductance and a 15% higher current-gain cutoff frequency, but exhibits a 38% poorer output conductance. Finally, we offer an analysis on the high-field transport properties of ultra-short gate-length AIInAs/GaInAs HEMT's. This analysis shows that a reduction of gate length from 150 to 50 nm neither enhances nor reduces their average velocity. In contrast, the addition of indium from 53% to 80% improves this parameter by 19%, from approximately 2.6 to 3.1 x lo7 cm/s.

Takens' theorem demonstrates that in the absence of noise a multidimensional state space can be reconstructed from a scalar time series. This theorem gives little guidance, however, about practical considerations for reconstructing a good state space. We extend Takens' treatment, applying statistical methods to incorporate the effects of observational noise and estimation error. We define the distortion matrix, which is proportional to the conditional covariance of a state, given a series of noisy measurements, and the noise amplification, which is proportional to root-mean-square time series prediction errors with an ideal model. We derive explicit formulae for these quantities, and we prove that in the low noise limit minimizing the distortion is equivalent to minimizing the noise amplification.

Purpose: The objective of this work was to demonstrate the feasibility of acquiring low-exposure megavoltage cone-beam CT (MV CBCT) threedimensional (3D) image data of sufficient quality to register the CBCT images to kilovoltage planning CT images for patient alignment and dose verification purposes.

Detection of infrared light is central to diverse applications in security, medicine, astronomy, materials science, and biology. Often different materials and detection mechanisms are employed to optimize performance in different spectral ranges. Graphene is a unique material with strong, nearly frequency-independent lightmatter interaction from far infrared to ultraviolet, with potential for broadband photonics applications. Moreover, graphene's small electron-phonon coupling suggests that hot-electron effects may be exploited at relatively high temperatures for fast and highly sensitive detectors in which light energy heats only the smallspecific-heat electronic system. Here we demonstrate such a hot-electron bolometer using bilayer graphene that is dual-gated to create a tunable bandgap and electrontemperature-dependent conductivity. The measured large electron-phonon heat resistance is in good agreement with theoretical estimates in magnitude and temperature dependence, and enables our graphene bolometer operating at a temperature of 5 K to have a low noise equivalent power (33 fW/Hz 1/2). We employ a pump-probe technique to directly measure the intrinsic speed of our device, >1 GHz at 10 K. Graphene, a two-dimensional (2D) hexagonal lattice of carbon, has remarkable electronic, thermal, and mechanical properties 1. Graphene's exceptional stiffness 2 leads to exceptionally low electron phonon interaction and high intrinsic mobility 3-6. Graphene's unique band structure 7 results in charge carriers which obey the massless Dirac equation in 2D 8,9 and gives rise to a quantized absorption coefficient which is frequency independent over a broad range from far infrared to ultraviolet 10,11. In this article, we exploit the small electron-phonon scattering 3 and broadband photon

Low-frequency 1/f noise is ubiquitous, and dominates the signal-to-noise performance in nanodevices. Here we investigate the noise characteristics of single-layer and bilayer graphene nanodevices, and uncover an unexpected 1/f noise behavior for bilayer devices. Graphene is a single layer of graphite, where carbon atoms form a 2D honeycomb lattice. Despite the similar composition, bilayer graphene (two graphene monolayers stacked in the natural graphite order) is a distinct 2D system with a different band structure and electrical properties. In graphene monolayers, the 1/f noise is found to follow Hooge's empirical relation with a noise parameter comparable to that of bulk semiconductors. However, this 1/f noise is strongly suppressed in bilayer graphene devices, and exhibits an unusual dependence on the carrier density, different from most other materials. The unexpected noise behavior in graphene bilayers is associated with its unique band structure that varies with the charge distribution among the two layers, resulting in an effective screening of potential fluctuations due to external impurity charges. The findings here point to exciting opportunities for graphene bilayers in low-noise applications. arXiv:0801.4576v1 [cond-mat.mtrl-sci] 29 Jan 2008 Ultra-thin graphite films have attracted strong scientific and technological interest as truly 2D transport systems [3, 4, 5] with exceptional carrier mobilities.[6, 7] While a singlelayer 2D graphene is a zero-gap semiconductor, which is not suitable for certain applications, a wealth of different band structures emerge in nanoscale graphene that exhibit band gaps and distinct electrical properties [8] desirable for various device applications, such as metallic interconnects, [7] field-effect transistors [9, 10] and single-charge devices. [4] In addition, both experimental [9, 11] and theoretical [12] studies have shown that the transport properties of

The APV25 is a 128-channel analogue pipeline chip for the readout of silicon microstrip detectors in the CMS tracker at the LHC. Each channel comprises a low noise amplifier, a 192-cell analogue pipeline and a deconvolution readout circuit. Output data are transmitted on a single differential current output via an analogue multiplexer. The chip is fabricated in a standard 0.25 mm CMOS process to take advantage of the radiation tolerance, lower noise and power, and high circuit density. Experimental characterisation of this circuit shows full functionality and good performance both in pre-and post-irradiation (20 Mrad) conditions. The measured noise is significantly reduced compared to earlier APV versions. A description of the design and results from measurements prior to irradiation are presented. #

There is a growing demand for low-power, small-size and ambulatory biopotential acquisition systems. A crucial and important block of this acquisition system is the analog readout front-end. We have implemented a low-power and low-noise readout front-end with configurable characteristics for Electroencephalogram (EEG), Electrocardiogram (ECG), and Electromyogram (EMG) signals. Key to its performance is the new AC-coupled chopped instrumentation amplifier (ACCIA), which uses a low power current feedback instrumentation amplifier (IA). Thus, while chopping filters the 1/f noise of CMOS transistors and increases the CMRR, AC coupling is capable of rejecting differential electrode offset (DEO) up to 50 mV from conventional Ag/AgCl electrodes. The ACCIA achieves 120 dB CMRR and 57 nV/ Hz input-referred voltage noise density, while consuming 11.1 A from a 3 V supply. The chopping spike filter (CSF) stage filters the chopping spikes generated by the input chopper of ACCIA and the digitally controllable variable gain stage is used to set the gain and the bandwidth of the front-end. The front-end is implemented in a 0.5 m CMOS process. Total current consumption is 20 A from 3V.

For the first time in vivo retinal imaging has been performed with a new compact, low noise Yb-based ASE source operating in the 1 µm range (NP Photonics, λ c = 1040 nm, ∆ λ = 50 nm, P out = 30 mW) at the dispersion minimum of water with ~7 µm axial resolution. OCT tomograms acquired at 800 nm are compared to those achieved at 1040 nm showing about 200 µm deeper penetration into the choroid below the retinal pigment epithelium. Retinal OCT at longer wavelengths significantly improves the visualization of the retinal pigment epithelium/choriocapillaris/choroid interface and superficial choroidal layers as well as reduces the scattering through turbid media and therefore might provide a better diagnosis tool for early stages of retinal pathologies such as age related macular degeneration which is accompanied by choroidal neovascularization, i.e. extensive growth of new blood vessels in the choroid and retina.

Significant progress has been made in systems that interpret the electrical signals of the brain in order to control an actuator. One version of these systems senses neuronal extracellular action potentials with an array of up to 100 miniature probes inserted into the cortex. The impedance of each probe is high, so environmental electrical noise is readily coupled to the neuronal signal. To minimize this noise, an amplifier is placed close to each probe. Thus, the need has arisen for many amplifiers to be placed near the cortex. Commercially available integrated circuits do not satisfy the area, power and noise requirements of this application, so researchers have designed custom integrated-circuit amplifiers. This paper presents a comprehensive survey of the neural amplifiers described in publications prior to 2008. Methods to achieve high input impedance, low noise and a large time-constant high-pass filter are reviewed. A tutorial on the biological, electrochemical, mechanical and electromagnetic phenomena that influence amplifier design is provided. Areas for additional research, including sub-nanoampere electrolysis and chronic cortical heating, are discussed. Unresolved design concerns, including teraohm circuitry, electrical overstress and component failure, are identified.

We present a compact integrated fiber laser with more than 200 mW of output power. It combines polarized fiber output with very narrow linewidth of less than 2 kHz. The coherence length of the laser is measured to be longer than 5 km. The laser features high mode stability of less than 10 MHz over hours. The relative intensity noise (RIN) spectrum is dominated by a peak at the relaxation oscillation frequency and is shot-noise limited otherwise. The RIN peak at 1 MHz is reduced to 130 dB Hz by integrating a negative feedback circuit. In addition to thermal wavelength tuning, the laser frequency can be modulated at a bandwidth of up to 10 kHz via the piezoelectric effect.

We report methodology that combines an ultrawide band multifrequency microwave system with technology of high magnetic fields for solving challenging problems in electron magnetic resonance (EMR) spectroscopy. This strategy has been made possible due to a novel EMR facility operating in an exceptionally wide range of microwave frequencies of 24 GHz to 3 THz, at magnetic fields up to 17 T, and in the temperature range of 1.6 to 330 K. The basic configuration of the multifrequency system works in a transmission mode and employs oversized cylindrical waveguides for routing the microwave power. A wide-band, low-noise, liquid helium cooled (4.2 K) InSb bolometer is used for signal detection. This approach results in an extremely wide-band performance, thus making it possible to employ a variety of solid-state millimeter and submillimeter microwave sources in combination with a far infrared laser microwave source for performing multifrequency EMR experiments. A complexity of resonant structures and related technical problems such as microphonics at high magnetic fields is virtually eliminated. The system is simple, yet sensitive, and has been revealed to be extremely advantageous while solving such problems as observation of AFMR transitions in spin-ordered systems, g-factor resolution enhancement in complex organic radicals, and resonance signal detection in EMR-silent spin systems having integer spin and large zero field splitting. A technical description of the multifrequency high-field EMR facility is presented and results of its performance tests are given. The potential utility of using the multifrequency high-field methodology in EMR studies is illustrated with selected examples of its recent applications.

A two-dimensional treatment of the potential distribution under the depletion approximation is presented for poly-crystalline silicon thin film transistors. Green's function approach is adopted to solve the two-dimensional Poisson's equation. The solution for the potential distribution is derived using Neumann's boundary condition at the silicon-silicon di-oxide interface. The developed model gives insight into device behavior due to the effects of traps and grainboundaries. Also short-channel effects and drain induced barrier lowering effects are incorporated in the model. The potential distribution and electric field variation with various device parameters is shown. An analysis of threshold voltage is also presented. The results obtained show good agreement with simulated results and numerical modeling based on the finite difference method, thus demonstrating the validity of our model.

A multi-fingerprint analysis is applied to the detection and attribution of anthropogenic climate change. While a single fingerprint is optimal for the detection of climate change, further tests of the statistical consistency of the detected climate change signal with model predictions for different candidate forcing mechanisms require the simultaneous application of several fingerprints. Model-predicted climate change signals are derived from three anthropogenic global warming simulations for the period 1880 to 2049 and two simulations forced by estimated changes in solar radiation from 1700 to 1992. In the first global warming simulation, the forcing is by greenhouse gas only, while in the remaining two simulations the direct influence of sulfate aerosols is also included. From the climate change signals of the greenhouse gas only and the average of the two greenhouse gasplus-aerosol simulations, two optimized fingerprint patterns are derived by weighting the model-predicted climate change patterns towards low-noise directions. The optimized fingerprint patterns are then applied as a filter to the observed near-surface temperature trend patterns, yielding several detection variables. The space-time structure of natural climate variability needed to determine the optimal fingerprint pattern and the resultant signal-tonoise ratio of the detection variable is estimated from several multi-century control simulations with different CGCMs and from instrumental data over the last 136 y. Applying the combined greenhouse gas-plus-aerosol fingerprint in the same way as the greenhouse gas only fingerprint in a previous work, the recent 30-y trends of annual mean near surface temperature are again found to represent a significant climate change at the 97.5% confidence level. However, using both the greenhouse gas and the combined forcing fingerprints in a two-pattern analysis, a substantially better agreement between observations and the climate model prediction is found for the combined forcing simulation. Anticipating

We discuss the potential benefits of using compound semiconductors for the detection of X-and gray radiation. While Si and Ge have become detection standards for energy dispersive spectroscopy in the laboratory, their use for an increasing range of applications is becoming marginalized by one or more of their physical limitations; namely the need for ancillary cooling systems or bulky cryogenics, their modest stopping powers and radiation intolerance. Compound semiconductors encompass such a wide range of physical properties that it is technically feasible to engineer a material to any application. Wide band-gap compounds offer the ability to operate in a wide range of thermal and radiation environments, whilst still maintaining sub-keV spectral resolution at hard X-ray wavelengths. Narrow band-gap materials, on the other hand, offer the potential of exceeding the spectral resolution of both Si and Ge, by as much as a factor of 3. Assuming that the total system noise can be reduced to a level commensurate with Fano noise, spectroscopic detectors could work in the XUV, effectively bridging the gap between the ultraviolet and soft X-ray wavebands. Thus, in principle, compound semiconductor detectors can provide continuous spectroscopic coverage from the far infrared through to gray wavelengths. However, while they are routinely used at infrared and optical wavelengths, in other bands, their development has been plagued by material and fabrication problems. This is particularly true at hard Xand gray wavelengths, where only a few compounds (e.g., GaAs, CdZnTe and HgI 2) have evolved sufficiently to produce working detection systems. In this paper, we examine the current status of research in compound semiconductors and by a careful examination of material properties and future requirements, recommend a number of compounds for further development. In the longer term, when material problems are sufficiently under control, we believe the future lies in the development of heterostructures and inserted interface layers to overcome contacting problems and quantum heterostructures and superlattices to facilitate low-noise readout.

K. WILHELM Max-Planck-Institut für Aeronomie, D-37189 Katlenburg-Lindau, Germany P. LEMAIRE Institut d'Astrophysique Spatiale, Unité Mixte CNRS – Université, Paris XI, Bat 121, F-91405 Orsay, France W. CURDT, U. SCH ¨UHLE and E. MARSCH Max-Planck-Institut für ...

We investigate the consequences of maximizing information transfer in a simple neural network (one input layer, one output layer), focussing on the case of non linear transfer functions. We assume that both receptive elds (synaptic e cacies) and transfer functions can be adapted to the environment.

We present a fully automated quantum key distribution prototype running at 625 MHz clock rate. Taking advantage of ultra low loss (ULL) fibres and low-noise superconducting detectors, we can distribute 6,000 secret bits per second over 100 km and 15 bits per second over 250km.

We have demonstrated a system capable of directly measuring the photon-number state of a single pulse of light using a superconducting transition-edge sensor microcalorimeter. We verify the photon-number distribution of a weak pulsed-laser source at 1550 nm. Such single-photon metrology at telecommunication wavelengths provides the foundation for ensuring the security of photon sources used in implementations of quantum cryptography. Additionally, this system has the lowest noise equivalent power of any single-photon detector and combines high efficiency near-infrared photon counting with the ability to resolve multiphoton absorption events.

We have studied an evolutionary prisoner's dilemma game with players located on two types of random regular graphs with a degree of 4. The analysis is focused on the effects of payoffs and noise (temperature) on the maintenance of cooperation. When varying the noise level and/or the highest payoff, the system exhibits a second order phase transition from a mixed state of cooperators and defectors to an absorbing state where only defectors remain alive. For the random regular graph (and Bethe lattice) the behavior of the system is similar to those found previously on the square lattice with nearest neighbor interactions, although the measure of cooperation is enhanced by the absence of loops in the connectivity structure. For low noises the optimal connectivity structure is built up from randomly connected triangles.

The theoretical existence of photon-number-splitting attacks creates a security loophole for most quantum key distribution (QKD) demonstrations that use a highly attenuated laser source. Using ultralow-noise, high-efficiency transition-edge sensor photodetectors, we have implemented the first version of a decoy-state protocol that incorporates finite statistics without the use of Gaussian approximations in a one-way QKD system, enabling the creation of secure keys immune to photon-number-splitting attacks and highly resistant to Trojan horse attacks over 107 km of optical fiber.

Recent developments in silicon based optoelectronics relevant to fiber optical communication are reviewed. Siliconon-insulator photonic integrated circuits represent a powerful platform that is truly compatible with standard CMOS processing. Progress in epitaxial growth of silicon alloys has created the potential for silicon based devices with tailored optical response in the near infrared. The deep submicrometer CMOS process can produce gigabits-per-second low-noise lightwave electronics. These trends combined with economical incentives will ensure that silicon-based optoelectronics will be a player in future fiber optical networks and systems.

The limits of the noise performance of detector readout front ends in CMOS technology have been studied. A theoretical minimal number of equivalent noise charge (ENC) that can be achieved by a CMOS technology is derived, taking both thermal noise and 1/f noise into account. Design criteria and techniques of CMOS readout front ends are presented so as to fully

Using experiments with anisotropic vibrated rods and quasi-2D numerical simulations, we show that shape plays an important role in the collective dynamics of self-propelled (SP) particles. We demonstrate that SP rods exhibit local ordering, aggregation at the side walls, and clustering absent in round SP particles. Furthermore, we find that at sufficiently strong excitation SP rods engage in a persistent swirling motion in which the velocity is strongly correlated with particle orientation.

We present a novel, noncontact method for the determination of quantitative optical properties of turbid media from 430 to 1050 nm. Through measuring the broadband reflectance from an unknown sample as a function of the spatial frequency of the projected illumination patterns, the absolute absorption and reduced scattering coefficients can be calculated without a priori assumptions of the chromophores present. This technique, which is called spatially modulated quantitative spectroscopy ͑SMoQS͒, was validated through the quantification of optical properties of homogenous liquid phantoms with known concentrations of absorbers and scatterers. The properties of the phantoms were recovered across the range of values prepared with R 2 values of 0.985 and 0.996 for absorption and reduced scattering, respectively. A measurement was also performed on skin tissue as a demonstration of the method's performance in vivo. The resultant absorption spectrum was well described by a multichromophore fit, and the quantitative values for oxy-and deoxyhemoglobin, water, and melanin were within published ranges for skin.

We investigate the behavior of discrete-time probabilistic cellular automata (PCA), which are Markov processes on spin configurations on ad-dimensional lattice, from a rigorous statistical mechanics point of view. In particular, we exploit, whenever possible, the correspondence between stationary measures on the space-time histories of PCAs on ℤd and translation-invariant Gibbs states for a related Hamiltonian on ℤ(d+1). This leads to a simple large-deviation formula for the space-time histories of the PCA and a proof that in a high-temperature regime the stationary states of the PCA are Gibbsian. We also obtain results about entropy, fluctuations, and correlation inequalities, and demonstrate uniqueness of the invariant state and exponential decay of correlations in a high-noise regime. We discuss phase transitions in the low-noise (or low-temperature) regime and review Toom's proof of nonergodicity of a certain class of PCAs.

The IRAM interferometer on Plateau de Bure has three 15 m diameter antennas presently equipped with low noise receivers for the 80-115 GHz band. Baselines extend 160 m north-south and 288 m east-west. There are two digital cross-correlators, a wide band continuum correlator ...

We report on a CMOS-based microelectrode array (MEA) featuring 11,011 metal electrodes and 126 channels, each of which comprises recording and stimulation electronics, for extracellular bidirectional communication with electrogenic cells, such as neurons or cardiomyocytes. The important features include: (i) high spatial resolution at (sub)cellular level with 3150 electrodes per mm 2 (electrode diameter 7 m, electrode pitch 18 m); (ii) a reconfigurable routing of the recording sites to the 126 channels; and (iii) low noise levels. Index Terms-CMOS-based microelectrode array (MEA), extracellular recording and stimulation, neuronal interface, reconfigurable switch matrix.

In this article we introduce a, video-rate, control system that can be used with any type of scanning probe microscope, and that allows frame rates up to 200 images/ s. These electronics are capable of measuring in a fast, completely analog mode as well as in the more conventional digital mode. The latter allows measurements at low speeds and options, such as, e.g., atom manipulation, currentvoltage spectroscopy, or force-distance curves. For scanning tunneling microscope ͑STM͒ application we implemented a hybrid mode between the well-known constant-height and constant-current modes. This hybrid mode not only increases the maximum speed at which the surface can be imaged, but also improves the resolution at lower speeds. Acceptable image quality at high speeds could only be obtained by pushing the performance of each individual part of the electronics to its limit: we developed a preamplifier with a bandwidth of 600 kHz, a feedback electronics with a bandwidth of 1 MHz, a home-built bus structure for the fast data transfer, fast analog to digital converters, and low-noise drivers. Future improvements and extensions to the control electronics can be realized easily and quickly, because of its open architecture with its modular plug-in units. In the second part of this article we show our high-speed results. The ultrahigh vacuum application of these control electronics on our ͑UHV͒-STM enabled imaging speeds up to 0.3 mm/ s, while still obtaining atomic step resolution. At high frame rates, the images suffered from noticeable distortions, which we have been able to analyze by virtue of the unique access to the error ͑dZ͒ signal. The distortions have all been associated with mechanical resonances in the scan head of the UHV-STM. In order to reduce such resonance effects, we have designed and built a scan head with high resonance frequencies ͑ജ64 kHz͒, especially for the purpose of testing the fast electronics. Using this scanner we have reached video-rate imaging speeds up to 200 frames/ s ͑5 ms/ image͒, while still obtaining atomically resolved structures.

The interest in accurate dosimetric measurements inside phantoms that simulate biological bodies has burgeoned since several regulatory commissions began calling for or recommending the testing for compliance with safety standards of low power devices. This paper presents a newly developed, robotbased system that allows automated E-field scanning in tissue simulating solutions. The distinguishing characteristics of the system are its high sensitivity and its broad dynamic range (1 pW/g)to 100 mW/g) over the entire frequency range (10 MHz to over 3 GHz) used for mobile communications. The reproducibility of the dosimetric evaluations has been shown to be considerably better than f5%. This has been accomplished by the use of an improved isotropic E-field probe connected to amplifiers with extremely low noise and drift characteristics in conjunction with digital processing of the data. Special emphasis has been placed on system reliability, user-friendliness and graphic visualization of data.

We establish an excess risk bound of O HR 2 n + √ HL * Rn for empirical risk minimization with an H-smooth loss function and a hypothesis class with Rademacher complexity Rn, where L * is the best risk achievable by the hypothesis class. For typical hypothesis classes where Rn = R/n, this translates to a learning rate of O (RH/n) in the separable (L * = 0) case and O RH/n + L * RH/n more generally. We also provide similar guarantees for online and stochastic convex optimization with a smooth non-negative objective.