DC SQUIDs as radiofrequency amplifiers

The optimization of radiofrequency amplifiers involving dc SQUIDs is discussed for both tuned and untuned input circuits. For a given frequency and input coil coupled to the SQUID, expressions are obtained for the optimum source resistance, gain, and noise temperature. The performance of two amplifiers designed according to these predictions is described. The gain of an untuned amplifier operated at 100 MHz and 4.2 K was 16.5±0.5 dB with a noise temperature of 3.8±0.9K; at 1.5 K the gain increased to 19.5±0.5 dB, while the noise temperature decreased to 0.9±0.4 K. A tuned amplifier operated at 93 MHz and 4.2 K had a gain of 18.6±0.5 dB and a noise temperature of 1.7±0.5 K. These results were in good agreement with predicted values.     

Synthetic aperture focusing technique signal processing

The synthetic aperture focusing technique (SAFT) is briefly reviewed and addressed as a heuristic digital ultrasonic imaging scheme which exploits the idea of back-propagating a set of measured and digitally stored A-scans. It is shown that for a far-field experimental set-up, ie for small, isolated defects remote to the transducer, SAFT reduces to the filtered back-projection imaging scheme which is well known within the framework of conventional X-ray computer tomography. Therefore, alternative data processing via Fourier transforms only, similar to the Fourier slice theorem of tomography, is possible, which sheds considerable light upon the heuristic SAFT pixel-space envelope-detection scheme. The resulting imaging identity has been termed POFFIS (physical optics far-field inverse scattering). The far-field assumption is then omitted yielding a Fourier-transform-SAFT algorithm (FT-SAFT) whose results are identical to back-propagation imaging with the definite advantage of fast processing capabilities based upon standard hardware and allowing immediate implementation of high resolution procedures as well as inclusion of mode-conversion effects; the theoretical background is pulse-echo diffraction tomography. The above results are supported and illustrated by application of all three algorithms — SAFT, POFFIS, FT-SAFT — to experimental data obtained from scanning a line aperture for several test specimens.     

Electrometric amplifiers with logarithmic characteristics

Conclusions Further work in the sphere of logarithmic amplifiers should be aimed at improving their metrological characteristics, investigating new logarithmic elements, studying the problem of their components' interchangeability, as well as developing and investigating new circuitry. For instance, according to the data of [27, 28], diffusion-type silicon transistors have an adequate logarithmic characteristic, however, they have not as yet been used in an electrometric amplifier owing to their special circuit requirements (a minimum resistance of their current source). It is probable that certain advantages, both with respect to the measurement error and the speed of operation, can be provided by electrometric amplifiers with a discretely formed logarithmic characteristic. These amplifiers are similar to the one described in [29] whose characteristic is formed by switching automatically feedback resistances by means of diodes which operate in a switching process.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 34–37, February, 1968.     

Photocompensated amplifiers with torsion-suspension galvanometers

Conclusions The above investigations have shown that in order to decrease drastically the galvanometer's sensitivity to shock it is necessary to suppress or prevent transverse oscillations of its moving part. This can be achieved by the use of transverse oscillation dampers.Magnetic induction dampers, for instance, can be used. Transverse oscillations occur almost exclusively in the direction of the least stiffness of suspensions, thus facilitating the design of magnetic induction dampers.However, liquid dampers seem to be more promising. Such damping can be achieved either by immersing the whole moving part in a liquid, or by means of concentrated drop dampers [7]. Preliminary experiments have shown the great efficiency of liquid dampers. It would appear that the use of such dampers in the control galvanometers of photocompensated systems will make it possible to use these instruments under the most difficult operating conditions.     

Magnetoresistive amplifiers with superconductive elements

The construction and properties of certain superconductive amplifiers in which the resistance of a gate element is controlled by the electromagnetic field of a signal coil are described in this paper. Vacuum-deposited films of tin, which have narrow resistive transition widths, have been used as the gate elements, and the field has been applied perpendicularly to the film surface. The parameters of small-signal analysis are determined, and the influence of temperature, bias magnetic field, and zero-signal gate current upon power gains are shown. The limitations and merits of the device in its present form are discussed.     

Extraction efficiency of saturated-gain high-power dye laser amplifiers: effect of nonlinear signal absorption

The effect of nonlinear signal absorption (NLSA) due to ground-state absorption and excited-state absorption in a transversely pumped high-power dye laser amplifier is theoretically examined with a one-dimensional steady-state model for a dye amplifier pumped by a copper vapor laser. A well-approximated analytical expression for the extraction efficiency is derived, from which the effect of NLSA in reducing the amplifier efficiency can be appreciated immediately and can also be interpreted in terms of certain characteristic lengths. The reduction in efficiency due to NLSA is found to be largely independent of the pump power, provided that the signal power is increased linearly with the pump power to continue to saturate the amplifier gain and suppress amplified spontaneous emission.     

Nanopillar arrays on semiconductor membranes as electron emission amplifiers

A new transmission-type electron multiplier was fabricated from silicon-on-insulator (SOI) material by integrating an array of one-dimensional (1D) silicon nanopillars onto a two-dimensional (2D) silicon membrane. Primary electrons are injected into the nanopillar-membrane (NPM) system from the flat surface of the membrane, while electron emission from the nanopillars is probed by an anode. The secondary electron yield (SEY) from the nanopillars in the current device is found to be about 1.8 times that of the plain silicon membrane. This gain in electron number is slightly enhanced by the electric field applied from the anode. Further optimization of the dimensions of the NPM and an application of field emission promise an even higher gain for detector applications and allow for probing of electronic/mechanical excitations in an NPM system stimulated by incident particles or radiation.     

Highly porous hydroxyapatite scaffolds with elongated pores using stretched polymeric sponges as novel template

This study reports a simple way of improving the compressive strength of highly porous hydroxyapatite (HA) scaffolds by adopting elongated polymeric sponges as a novel template. In this method, as-received polymeric sponges with isotropic pores were stretched uniaxially to 50% elongation at 200 °C for 2 h, and then coated with a HA slurry. The HA-coated sponges were heat-treated at 800 °C for 3 h to remove the polymeric sponges and at 1250 °C for 3 h to sinter the HA walls. The fabricated samples showed a highly anisotropic pore structure with elongated pores parallel to the direction of the elongation of the polymeric sponge. This simple method allowed a highly porous scaffold to have a high compressive strength of 3.8 ± 0.1 MPa at a porosity of 76% when tested parallel to the direction of pore elongation.     

Dispersible gold nanorod dimers with sub-5 nm gaps as local amplifiers for surface-enhanced Raman scattering

We report the synthesis of solution-dispersible, 35 nm diameter gold nanorod dimers with gaps as small as ～2 nm for surface-enhanced Raman scattering (SERS). Using on-wire lithography (OWL), we prepared tailorable dimers in high yield and high monodispersity (～96% dimers) that produce both large and reproducible SERS signals with enhancement factors of (6.8 ± 0.7) × 10(8) for single dimers in air and 1.2 × 10(6) for ensemble-averaged solution measurements. Furthermore, we show that these structures, which are the smallest ever made by OWL, can be used to detect molecules on flat surfaces and in aqueous solutions. When combined, these attributes with respect to sensitivity, reproducibility, and tailorability lead to a novel and powerful local amplification system for SERS applications.     

Training an asymmetric signal perceptron through reinforcement in an artificial chemistry

State-of-the-art biochemical systems for medical applications and chemical computing are application-specific and cannot be reprogrammed or trained once fabricated. The implementation of adaptive biochemical systems that would offer flexibility through programmability and autonomous adaptation faces major challenges because of the large number of required chemical species as well as the timing-sensitive feedback loops required for learning. In this paper, we begin addressing these challenges with a novel chemical perceptron that can solve all 14 linearly separable logic functions. The system performs asymmetric chemical arithmetic, learns through reinforcement and supports both Michaelis–Menten as well as mass-action kinetics. To enable cascading of the chemical perceptrons, we introduce thresholds that amplify the outputs. The simplicity of our model makes an actual wet implementation, in particular by DNA-strand displacement, possible.     

Water as reactive gas to prepare titanium oxynitride thin films by reactive sputtering

Thin films of titanium oxynitride were successfully prepared by dc reactive magnetron sputtering using a titanium metallic target, argon, nitrogen and water vapour as reactive gases. The nitrogen partial pressure was kept constant during every deposition whereas that of the water vapour was systematically changed from 0 to 0.1 Pa. The evolution of the deposition rate with an increasing amount of water vapour injected into the process was correlated with the target poisoning phenomenon estimated from the target potential. Structure and morphology of the films were analysed by X-ray diffraction and scanning electron microscopy. Films were poorly crystallised or amorphous with a typical columnar microstructure. Nitrogen, oxygen and titanium concentrations were determined by Rutherford backscattering spectroscopy and nuclear reaction analysis, and the amount of hydrogen in the films was also quantified. Optical transmittance in the visible region and electrical conductivity measured against temperature were gradually modified from metallic to semiconducting behaviour with an increasing supply of the water vapour partial pressure. Moreover, an interesting maximum of the electrical conductivity was observed in this transition, for a small amount of water vapour.     

Design and implementation of cryogenic semiconductor amplifiers as interface between RSFQ circuits

Rapid single flux quantum (RSFQ) circuits create high interest in cryogenic amplifiers as interface to commercial room temperature electronics. The requirements for the amplifiers are an extremely high bandwidth (SFQ pulses with ), high voltage gain of about 10⁴ (common RSFQ output voltage level of about ), low power consumption (cryogenic environment at 4 K) and low noise. Hybrid amplifiers, based on commercial available p-HEMT transistors, can solve the problematic high-speed interface. In this paper, we present measurement results of a hybrid four stage coplanar amplifier in combination with a RSFQ Toggle Flip-Flop (RSFQ T-FF) and a Josephson array quantizer (JA-Q).     

Fabrication of three dimensional polymeric scaffolds with spherical pores

This paper reports polymeric scaffolds with spherical internal macropores and relatively large external dimension. Paraffin spheres with the diameter of several hundred microns were prepared by a suspension technique. Particulate leaching technique based on this kind of spherical porogens was combined with room-temperature compression molding technique to fabricate biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) porous scaffolds potentially for tissue engineering or in situ tissue induction. The scaffolds exhibited ordered macropores with good pore interconnectivity. The porosity ranged from 80 to 97% adjusted simply by varying porogen content. The foams with porosity around 90% have compressive modulus over 3 MPa and compressive strength over 0.2 MPa. As preliminary cell experiments with 3T3 fibroblasts cultured on the porous scaffolds indicate, the processing procedure of the scaffolds has not brought with problem in cytotoxicity.     

Synthesis of mesoporous Fe-incorporated alumina particles with regular pores

The incorporation of iron species content up to 20 at.% in the framework of alumina containing silica has been successfully synthesized by using citric acid and an ultrasonic spray method under high acidic condition. In general, it is difficult to introduce the Fe ions into the mesopore-framework directly because of a fast dimerization rate of Fe ions. Moreover, the mesoporous alumina particle incorporating iron up to 20 at.% has not been reported yet. In this work, the pore structure of the prepared samples is hexagonal with regular pores and no agglomeration of iron oxide particles shows in the samples. This material can be a potential catalyst for selective reduction, hydrocarbon oxidation and redox reaction at high temperature.     

Diffuse X-ray scattering from a crystal with spheroidal pores

A theory of diffuse X-ray scattering from a crystal with spheroidal pores has been developed. Expressions for the Debye-Waller factor, intrinsic correlation function, and correlation volume have been derived. Reciprocal-space maps of the diffuse scattering have been numerically simulated for model crystals with pores having the shapes of spheroids and rectangular parallelepipeds. It is established that the pore size fluctuations influence the angular distribution of X-ray scattering intensity in the reciprocal space.