Biosorption characteristics of Bacillus sp. ATS-2 immobilized in silica gel for removal of Pb(II)

The bacterial strain Bacillus sp. ATS-2 isolated from Pb(II) polluted soil was immobilized with a silica matrix and Pb(II) biosorption properties of immobilized biosorbent were examined. Optimum biosorption conditions were investigated in the fixed bed column with the variation in the parameters of pH, bed length, flow rate and influent concentration. The Pb(II) biosorption equilibrium was attained within 60 min and the maximum biosorption yield for silica gel immobilized Bacillus sp. ATS-2 was determined as 91.73% at pH 4.0. The higher biosorption yields were observed at flow rates of 60 and 180 ml h(-1). The optimum bed length for the column was found as 10 cm. Data obtained from batch studies were evaluated by Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherm models. The maximum monolayer capacity of Bacillus sp. ATS-2 for Pb(II) was 2.36 x 10(-5) mol g(-1). The involvement of the functional groups on the surface of immobilized cells in biosorption process was also evaluated by FTIR spectral analysis.     

Investigation and comparison between new satellite impact test results and NASA standard breakup model

This paper summarizes two new satellite impact tests conducted in order to investigate on the outcome of low- and hypervelocity impacts on two identical target satellites. The first experiment was performed at a low velocity of 1.5 km/s using a 40-g aluminum alloy sphere, whereas the second experiment was performed at a hypervelocity of 4.4 km/s using a 4-g aluminum alloy sphere, by a two-stage light gas gun. To date, approximately 1500 fragments from each impact test have been collected for detailed analysis. Each piece was analyzed based on the method used in the NASA standard breakup model 2000 revision. The detailed analysis will conclude (1) the similarity in mass distribution of fragments between low- and hypervelocity impacts encourages the development of a general-purpose mass-based distribution model applicable for a wide impact velocity range, and (2) the difference in area-to-mass ratio distribution between the impact experiments and the NASA standard breakup model suggests to describe the area-to-mass ratio by a bi-normal distribution.     

Approximate analysis of serial flow lines with multiple parallel-machine stations

This paper studies serial flow lines, in which each station consists of multiple identical reliable parallel machines. The parallel machines of different work stations are not necessarily identical, viz., station processing times are assumed to be exponentially distributed with non-identical mean service rates. Initially, a model consisting of two stations with multiple parallel machines and an intermediate buffer is solved analytically, by developing a recursive algorithm that generates the transition matrix for any value of the intermediate buffer capacity. This model is used as a decomposition block for solving larger lines. More specifically, the decomposition block is solved via exact Markovian analysis and then the decomposition equations and an algorithm that simultaneously solves them are derived in order to evaluate the performance measures of large production systems with multiple parallel-machine stations. Numerical results are provided for large production lines with up to 1000 workstations. These results are compared against simulation and the average percentage error is found to be very small.     

5 GHz low power frequency synthesiser with dual-modulus counter

A 5 GHz low power frequency synthesiser with a dual-modulus counter (DMC) was fabricated in 0.18 μm CMOS technology. The DMC allows to reduce the power consumption and to provide the functionality of the divider without a swallower counter. The settling time takes no more than 5 μs with an adaptive bandwidth topology. The measured phase noise is -87 dBc/Hz and -119 dBc/Hz at 10 kHz and 1 MHz offset frequencies, respectively. The reference spurs level is lower than -55 dBc at 10 MHz offset. The proposed synthesiser covers frequencies between 5.14 and 5.86 GHz in steps of 20 MHz and consumes 16.4 mW at 1.5 V supply voltage.     

异步应答激光测距技术

异步应答激光测距可实现卫星距离及星地时差测量.本文给出的主波时差公式与经典公式,以及一种拟工程实现、且与异步应答激光测距原理相同的无线电测距方法给出的工程应用公式不同.为了探求正确的主波时差公式,掌握这种测距体制的测距精度,进而验证异步应答激光测距体制的工程可行性,本文设计并开展了异步应答激光测距技术验证实验,利用两个地面测距终端对卫星反射测距模拟了星地异步应答激光测距过程.该实验是我国对异步应答激光测距体制的首次实践.实验研究结果表明,异步应答激光测距可用于两终端之间距离和主波时差的精确测量,且本文给出的主波时差公式正确,经典公式与应用公式存在不妥之处.     

On control strategies in a multi-stage production system

A multi-stage production system is composed of a set of stations, each station performing a given task, and a set of vehicles, each vehicle moving between two successive stations. A station can choose a buffer or a kanban mechanism for controlling the work-in-process (WIP) in the station. A vehicle can choose a push or a pull policy for carrying parts from its upstream station to its downstream station. A control strategy is formed by combining the WIP mechanisms adopted in all stations and the carrying policies employed by all vehicles. The production system is modelled as a queuing system. Some structural properties of performance measures are characterized. We develop a decomposition approach for large systems, which performs very well. We determine the optimal numbers of buffers or kanbans at all stations in the design period, and the optimal control strategy during operation. Many numerical computations are given for evaluating the efficiencies of the decomposition approach and optimization methods, and further providing some intuitions and insights.     

Space-based augmentation for global navigation satellite systems

This paper describes space-based augmentation for global navigation satellite systems (GNSS). Space-based augmentations increase the accuracy and integrity of the GNSS, thereby enhancing users' safety. The corrections for ephemeris, ionospheric delay, and clocks are calculated from reference station measurements of GNSS data in wide-area master stations and broadcast via geostationary earth orbit (GEO) satellites. This paper discusses the clock models, satellite orbit determination, ionospheric delay estimation, multipath mitigation, and GEO uplink subsystem (GUS) as used in the Wide Area Augmentation System developed by the FAA.     

单片机控制的高精度Michelson干涉型波长计

设计了Ⅻehelson干涉型激光波长计干涉条纹的单片微机计数硬件电路，编写了8254计数和KeilC51波长运算程序．为提高仪器的测量精度，在硬件和软件上提出了新的设计方案．两个8254计数器可以在单片微机的控制下自动从参考光脉冲信号的下降沿开始对参考信号和被测信号同时计数；参考激光干涉条纹计数满1500000后。参考信号和被测信号的计数器可以同时被自动锁定；单片微机得到锁定信号后，完成两个计数值的读取、波长运算、10次移位平均和7位波长显示．对633nm和532nm两种稳频激光波长进行了实际测量，测量数据表明该计数系统使波长的测量精度达到2×10^-7．     

Telstar Time Synchronization

A broad-band completely reciprocal transmission path across the Atlantic was made available for the first time by the Telstar I satellite. In August, 1962, the U. S. Naval Observatory (USNO) and the National Physical Laboratory (NPL) cooperated in an experiment using the satellite to relate the master clocks at the USNO, and the Royal Greenwich Observatory (RGO) at Herstmonceux, U. K. Pulsed signals, 5 ?s long, at the rate of ten per second were transmitted simultaneously over the satellite circuit from the ground stations at Andover, Me. and Goonhilly Downs, Cornwall, U. K. The time difference between received and transmitted pulses was measured at each station and from these results the relative setting of the station clocks was obtained directly. In the final experiment on August 27th, the Goonhilly clock was found to be 72.6±0.8 ?s ahead of Andover. The internal consistency of the results was checked by comparing the measured time delays of the signals over whole or part of the path with the value calculated from the satellite ephemeris, based entirely on Minitrack observations. The measured time delays were consistent to ±1 ?s and did not differ from the ephemeris by more than 6 ?s, equivalent to 1 km error in range. The time synchronization between the ground stations was extended to the observatory clocks by low-frequency ground-wave signals propagating with known velocities.     

The charges,currents and near‐field characteristics of the transparent source for the FDTD method

Abstract

The electromagnetic characteristics of a transparent source for the finite‐difference time‐domain (FDTD) method are investigated. The approximate formulations for the corresponding electric and magnetic fields at the source are first reported, while the associated charges and current are also demonstrated. The approximate E field and H field are very closely related to the FDTD simulated results. It is shown that the magnetic field is proportional to the temporal derivative of the electric field at the source node, while the electric field is proportional to the temporal integration of the driving function. Static charges may be built up to produce static E fields after the driving function has passed, which are responsible for the dc offset problem in the pulsed FDTD algorithm. The dc offset is verified for the case of Gaussian pulse excitation and is avoided via the use of a bipolar pulse.     

Heavy traffic analysis of a single vehicle loop in an automated storage and retrieval system

We consider an automated storage/retrieval system in which cargo moves between the storage/retrieval machines and the system entrance/exit stations through a single automated vehicle loop. Past studies indicated that the cargo waiting time in the loop is affected by the dispatching rules, which govern the sequence of the cargo to be handled. In this paper, we show that the loop configuration, which has received little research attention, also has a big impact on the cargo waiting time. When the first-come-first-served dispatching rule is used, we derive the relationship between the number of stations and the ratio of the average cargo retrieval time to the average cargo storage time. When the first-encountered-first-served dispatching rule is used, we show that even the arrangement of the input channel and the output channel of a station can have significant impact on the cargo waiting time. Furthermore, we derive a formula for the vehicle visit rate for each station under heavy traffic conditions. This formula helps to explain the phenomenon that the waiting times at different stations can be very different even when the loop is symmetrically designed and the cargo arrival rates to the stations are similar. In addition to analytical models, we use simulations to evaluate the performance of different loop configurations. Our research suggests that a substantial improvement can be achieved by making proper adjustments to the loop configuration.     

Trigger electronics of the new Fluorescence Detectors of the Telescope Array Experiment

The Telescope Array Project is an experiment designed to observe Ultra High Energy Cosmic Rays via a “hybrid” detection technique utilizing both fluorescence light detectors (FDs) and scintillator surface particle detectors (SDs). We have installed three FD stations and 507 SDs in the Utah desert, and initiated observations from March 2008. The northern FD station reuses 14 telescopes from the High Resolution Fly's Eye, HiRes-I station. Each of the two southern FD stations contains 12 new telescopes utilizing new FADC electronics. Each telescope is instrumented with a camera composed of 256 PMTs. Since the detectors are composed of many PMTs and each PMT detects fluorescence photons together with the vast amount of night sky background, a sophisticated triggering system is required. In this paper, we describe the trigger electronics of these new FD stations. We also discuss performance of the FDs with this triggering system, in terms of efficiencies and apertures for various detector configurations.     

A high background rejection method in a proportional counter using field-adjusting electrodes as guard cathodes

A single anode single large cell counter, with veto-counters around it, is described. To get uniform response of the pulse height and the energy resolution, the counter has field-adjusting electrodes at the end walls of the anode wire, and these electrodes are also used to reject the background events which are caused by cosmic rays passing through near the end walls of the anode.A rocket flight experiment showed that the combination of rise time discrimination and anti-coincidence method reduced the cosmic ray induced background events to a level of 1.2×10^?4 counts s^?1 cm^?2 keV^?1 in the energy range of 2–40 keV, which represented an overall background reduction of 98% in this energy range.     

Design and testing of a new stand for the BOMAB family of phantoms

A new stand has been designed to support the Bottle Manikin Absorber Phantoms when the phantoms are counted in the vertical position in a whole-body counter. The stand previously used by the Human Monitoring Laboratory was constructed from metal and was heavy to transport and making height adjustments to accommodate different phantom sizes was very time consuming. The new stand is constructed from lightweight plastic materials and allows easy height adjustments to accommodate different phantom sizes while supporting the weight of the phantoms. The stand was evaluated inside a whole-body counter at a nuclear-generating station and met all operational requirements for accessibility and ease of use.     

NASA utilization of ISS -past, present and future

Construction of International Space Station (ISS) began in 1998, with permanent human occupancy commencing in late 2000. The first NASA research experiment reached ISS in September 2000. The February 2001 launch of the US Laboratory Destiny enabled the gradual outfitting of the module with research facilities and heralded the start of continuous research operations in March 2001. Initially, the NASA utilization program consisted of basic and applied peer-reviewed research in a variety of research disciplines. Between March 2001 and June 2002, as assembly of the station continued, Destiny was outfitted with seven research racks, launched on the Space Shuttle, to support the planned investigations, also transported to and from ISS on the Shuttle. The Columbia accident in February 2003 grounded the Shuttle fleet for more than two years, during which time NASA relied on Russian vehicles for transportation of research material. This along with the reduction of the ISS crew size from three to two, dramatically impacted the research conducted. The January 2004 announcement of the Vision for Space Exploration significantly altered the focus of NASA’s ISS utilization program toward developing medical countermeasures and using ISS as a technology testbed for exploration missions. The resumption of Shuttle flights in July 2005 also resumed the outfitting of Destiny with research racks, with the subsequent return of ISS crew size to three and resumption of ISS assembly. In late 2007-early 2008, we will see the addition of the European Columbus module, with its five research racks and two external payloads, followed by the Japanese Kibo pressurized modules, with two research racks, and the Canadian dexterous robotic arm. Subsequent Shuttle flights will deliver more NASA racks, the Japanese external pay-load platform and NASA external payloads while Japanese H-II Transfer Vehicles (HTV) will deliver racks and external pay-loads. Significant international collaboration is anticipated. Sometime in 2009, the infrastructure should be in place to enable the ISS crew size to increase to six, expanding the capability to conduct research. With the retirement of the Space Shuttle in late 2010, NASA will once again rely on partner vehicles for transportation until a commercial transportation system and the Crew Exploration Vehicle are in place early in the next decade.     

One-way time transfer using geostationary satellite TDF2

The way that geostationary television satellites can easily be used to perform common-view time transfer between remote clocks is presented. Different parameters and sources of error that have to be kept under control in order to achieve time transfer with a precision of 10 ns is reviewed. Two different methods are elaborated to eliminate the influence of satellite residual motion with a final precision that can reach 10 ns. Experimental results obtained on common-view time transfer measurements using the TV satellite TDF2 between four French laboratories show that frequency transfer can be performed with a stability of 1 part in 10¹⁴ for an averaging time of 10 days. The comparison of time transfer results with accurate common-view GPS data available between the four stations and with orbit data provided by the CNES showed measurement biases that are most likely due to errors in the antenna coordinates     

Field-programmable-gate-array-based time-to-digital converter with200-ps resolution

A new design of a time-to-digital converter (TDC) implemented on an FPGA chip with amorphous antifuse structures is presented. Time coding with 200-ps resolution (LSB), 10-ns range, and very short conversion time is realized by two tapped delay lines working in-a differential mode. Thanks to the local feedback loops, the output from the delay line is obtained directly in “1-out-of-N” code and then converted to 6-bit natural binary. Within the temperature range from 0°C to 45°C, the time offset at the output is constant, the resolution changes by ±0.02 LSB, and the offset-corrected integral linearity error is less than 1 LSB     

An experimental study of flux presetting-resetting characteristics of magnetic cores with rectangular hysteresis loop

When magnetic cores with a square hysteresis loop are used for a time delay Crcuit or a pulse counter circuit, and if these circuits are designed by the use of the static hysteresis loop, the ac magnetization curve, or the control magnetization curve (CMC) which is the basic characteristic of a magnetic amplifier, there is apt to be a marked discrepancy between their design values and measured values. Since, in the flux control of magnetic cores used for a time delay circuit or a pulse counter circuit, the flux, contrary to the case with a magnetic amplifier, arrives at the negative saturation from the positive saturation by many intermittent signal voltages, a new characteristic quite different from CMC and other characteristics must be adopted as the standard of the design in this case. It was for this reason that instantaneous relation between the rate of flux change and the exciting current was examined in the case in which real flux resetting behaviors of a time delay circuit or a pulse counter circuit were taken into consideration, by using grain-oriented 50 per cent permalloy as the sample, with a view to obtaining core characteristics serviceable enough for exact design methods of a time delay circuit or a pulse counter circuit. Various useful results have been obtained as to: 1) how the correlation between rate of flux changedPhi/dtand instantaneous values of exciting current icchanges in proportion to the flux values, 2) how the amount of reset fluxDeltaPhi_{r}will change according to the flux valuePhiand the rate of flux changedPhi/dt, and 3) how the above-mentioned relations are connected to the tape thickness of the magnetic core. This paper reports the results of this investigation.     

Nanoparticle transport in conical-shaped nanopores

This report presents a fundamental study of nanoparticle transport phenomena in conical-shaped pores contained within glass membranes. The electrophoretic translocation of charged polystyrene (PS) nanoparticles (80- and 160-nm-radius) was investigated using the Coulter counter principle (or "resistive-pulse" method) in which the time-dependent nanopore current is recorded as the nanoparticle is driven across the membrane. Particle translocation through the conical-shaped nanopore results in a direction-dependent and asymmetric triangular-shaped resistive pulse. Because the sensing zone of conical-shaped nanopores is localized at the orifice, the translocation of nanoparticles through this zone is very rapid, resulting in pulse widths of ~200 μs for the nanopores used in this study. A linear dependence between translocation rate and nanoparticle concentration was observed from 10(7) to 10(11) particles/mL for both 80- and 160-nm-radius particles, and the magnitude of the resistive pulse scaled approximately in proportion to the particle volume. A finite-element simulation based on continuum theory to compute ion fluxes was combined with a dynamic electric force-based nanoparticle trajectory calculation to compute the position- and time-dependent nanoparticle velocity as the nanoparticle translocates through the conical-shaped nanopore. The computational results were used to compute the resistive pulse current-time response for conical-shaped pores, allowing comparison between experimental and simulated pulse heights and translocation times. The simulation and experimental results indicate that nanoparticle size can be differentiated based on pulse height, and to a lesser extent based on translocation time.     

An averaging mode time-to-amplitude converter with picosecondresolution

A time-to-amplitude converter (TAC) meant to be employed in pulsed time-of-flight (TOF) laser rangefinding and capable of operating at a very high pulse repetition rate (PRR) is described. It is based on a precise time interval between the emitted light pulses and measures the phase difference of the logic-level pulse trains formed by timing pulses derived from the transmitted and received light pulses. The fast part of the TAC is constructed by means of ECL 100 K circuits. Test results indicate that the TAC is well suited for fast, millimeter-level resolution applications, and a full width at half maximum (FWHM) resolution of 1.0 ps is achieved with a 5-MHz pulse repetition rate and 0.1-Hz-10-kHz measurement bandwidth