Magnetically-coupled piston pump for high-purity gas applications

Experiments based on noble elements such as gaseous or liquid argon or xenon utilize the ionization and scintillation properties of the target materials to detect radiation-induced recoils. A requirement for high light and charge yields is to reduce electronegative impurities well below the ppb (parts per billion, 1 ppb \(=1\times 10^{-9}\) mol/mol) level. To achieve this, the target material is continuously circulated in the gas phase through a purifier and returned to the detector. Additionally, the low backgrounds necessary dictate low-Rn-emanation rates from all components that contact the gas. Since commercial pumps often introduce electronegative impurities from lubricants on internal components or through small air leaks, and are not designed to meet the radiopurity requirements, custom-built pumps are an advantageous alternative. A new pump has been developed in Muenster in cooperation with the nEXO group at Stanford University and the nEXO/XENON group at Rensselaer Polytechnic Institute based on a magnetically-coupled piston in a hermetically sealed low-Rn-emanating vessel. This pump delivers high performance for noble gases, reaching more than 210 standard liters per minute (slpm) with argon and more than 170 slpm with xenon while maintaining a compression of up to 1.9 bar, demonstrating its capability for noble gas detectors and other applications requiring high standards of gas purity.     

Method for generating a low-voltage pulsed arc in gas: Study of the influence of the circuit parameters

A novel method for generating a pulsed arc in gas is considered. The method can be used in devices in which rapid and efficient heating of the working gaseous medium is required. Electric circuits for generating pulsed arcs are analyzed. For the chosen discharge circuit, the dynamics of energy release in the column of a pulsed arc is experimentally investigated. Methods for estimating the discharge circuit parameters are proposed. Results of estimating these parameters in an existing experimental device are presented.     

A high-temperature laser ion source for trace analysis and other applications

We report here on the development of a high-temperature laser ion source useful for trace analysis and other applications. It consists of a high temperature ionization chamber, three tunable dye lasers pumped by copper vapor lasers for stepwise resonant ionization and a Mattauch-Herzog mass spectrometer for the analysis of photo-ions. The principle of the laser ion source and its theoretical efficiency are discussed, where the efficiency of a laser ion source is the ratio of photo-ions extracted out to the number of atoms introduced into the cavity. Experimentally, an efficiency of 2×10^–3 has been achieved for technetium. The scheme of gated detection is described which is used for suppressing isobaric background of molybdenum. The possible improvements are briefly mentioned for achieving isotopic analysis of 10⁸ atoms of ^97,98Tc in the presence of 10¹⁵ atoms of molybdenum, as separated chemically from molybdenum ore. Such an analysis of technetium isotopes produced in molybdenite ore by a (v,e ^–) reaction, is expected to yield information about the solar neutrino flux.Permanent address: Bhabha Atomic Research Centre, Bombay 400085, India     

Reduction theory for symmetry breaking with applications to nematic systems

We formulate Euler–Poincaré and Lagrange–Poincaré equations for systems with broken symmetry. We specialize the general theory to present explicit equations of motion for nematic systems, ranging from single nematic molecules to biaxial liquid crystals. The geometric construction applies to order parameter spaces consisting of either unsigned unit vectors (directors) or symmetric matrices (alignment tensors). On the Hamiltonian side, we provide the corresponding Poisson brackets in both Lie–Poisson and Hamilton–Poincaré formulations. The explicit form of the helicity invariant for uniaxial nematics is also presented, together with a whole class of invariant quantities (Casimirs) for two-dimensional incompressible flows.     

一种用于弧流电源的新型打坑电路设计

作为中性束注入加热系统的核心设备,弧流电源的性能至关重要。打坑电路是弧流电源的重要组成部分,其动态响应特性及稳定性决定了弧流电源的性能。提出了一种用于弧流电源的新型打坑电路解决方案,能在150 μs内快速实现大电流的跌落和恢复,并且跌落和恢复过程中基本无过冲,用于转移的电子开关(比如IGBT)在开关过程中过电压小,可靠性高,吸收电路容易实现。该方案可以很好地替代传统的弧流电源打坑电路。     

Carbon-iron arc plasma: Characterization and novel applications

The paper presents some novel applications of an arc plasma related to the synthesis of carbon nanostructures. The influence of iron on the final composition of solid products (e.g. fullerene content) is discussed. Pure and Fe-doped carbon plasmas were characterized by the optical emission spectroscopy. Dedicated to Prof. Jan Janča on the occasion of his 60th birthday. This work was supported by the funds of the State Committee for Scientific Research through the Department of Chemistry, Warsaw University within the project No. BW-1383/31/97 (to H.L.) and the grant No. 3 T09A 087 13 (to P.B.).     

Turbulence and wave breaking effects on air-water gas exchange

The relation between Ising spin systems and public-key cryptography is investigated using methods of statistical physics. The insight gained from the analysis is used for devising a matrix-based cryptosystem whereby the ciphertext comprises products of the original message bits; these are selected by employing two predetermined randomly constructed sparse matrices. The ciphertext is decrypted using methods of belief propagation. The analyzed properties of the suggested cryptosystem show robustness against various attacks and competitive performance to modern cryptographical methods.     

Characterization of a ferrofluid-based thermomagnetic pump for microfluidic applications

We experimentally characterize the performance of a miniature thermomagnetic pump, where suitably imposed temperature and magnetic field gradients are used to drive ferrofluid in a 2 mm diameter glass capillary tube, without application of any external pressure gradient. Such a pump can operate in a hermetically sealed micro electromechanical system configuration without any moving part, and is thus capable of handling microfluidic samples with little risk of contamination. In the experiment, the ferrofluid in the capillary is exposed to a magnetic field using a solenoid; a small resistive heater wrapped on the tube wall is used to create temperature gradient in such a way that the Kelvin body force in the medium produces a net unbalanced axial component. This causes a thermomagnetic pumping action, transporting the ferrofluid in the capillary tube from the colder end to the warmer end. Performance of the thermomagnetic pump is investigated experimentally to characterize the pump pressure head and discharge under different working conditions, namely, the magnetic field strength, heating power, and ferrofluid properties. A comparison with two other field actuation pumps at comparable length scales is also presented. The pump produces higher output at lower power supplies and magnetic field compared to the other two pumps.     

A Brownian-ratchet DNA pump with applications to single-nucleotide polymorphism genotyping

We have fabricated a micron-scale device capable of transporting DNA oligomers using Brownian ratchets. The ratchet potential is generated by applying a voltage difference to interdigitated electrodes. Cycling between the charged state and a discharged, free-diffusion state rectifies the Brownian motion of charged particles. The observed macroscopic transport properties agree with the transport rate predicted from microscopic parameters including the DNA diffusivity, the dimensions of the ratchet potential, and the cycling time. Applications to human genetics, primarily genotyping of single-nucleotide polymorphisms (SNPs), are discussed. Received: 7 November 2001 / Accepted: 14 January 2002 / Published online: 22 April 2002     

A systematics for Zweig rule breaking

In the framework of a simple model, rough magnitudes of all Zweig suppressed decays are described in terms of a few mixing angles $\text{θ}{}_{\mathrm{<mtext>N</mtext>}}{}^{\mathrm{\psi }}\text{～}\text{1}\text{2000}$, $\text{θ}{}_{\mathrm{<mtext>c</mtext>}}{}^{\mathrm{<mtext>\omega ,\phi ,\eta \; ～</mtext><mtext>1</mtext><mtext>50</mtext>}}$, . The hierarchy of these mixing angles are seen to agree with the systematics, suggested by the dynamical mechanisms.     

Charged spray generation for gas cleaning applications

The paper presents results of experimental investigation of properties of charged sprays generated by two types of pressure atomizers with charging by induction. Among other possible methods of charged spray generation, the induction charging has been considered due to its most practical importance. The goal of this research is to optimise the charging process with respect to obtain droplets of required size and charge for their application for exhaust gas cleaning from submicron particles in electrostatic scrubber used for the removal of PM from Diesel engine exhausts. Electrostatic scrubbers use electrostatic forces in order to deposit fine charged particles onto oppositely charged droplets.     

忆阻电路的基本性质及其应用

对有边界的忆阻元件与电容、 电感的串、 并联电路分别进行了研究, 分析了电路所具有的特性和频率及元件的电容、 电感对电路的影响, 通过仿真验证了理论结果.根据有边界的忆阻元件及其构成电路的性质研究, 对其潜在的应用进行了预测.     

Scope for industrial heat pump applications in the United States

Two major criteria for successful heat pump installations in process plants are the “appropriate placement” and “appropriate sizing” of the heat pump, consistent with the thermodynamics of the process. Failure to fulfil these conditions will result in the heat pump not achieving the anticipated savings and may even cause a net increase in process energy costs.This paper outlines a study in which the proven thermodynamics-based techniques of pinch technology were used to evaluate the scope for heat pumping in a range of industrial processes of significance in the United States. The procedures used in the study are presented together with the results obtained from the work. Implications for future heat pump applications in the United States are also described.     

Determination of the equivalent circuit of gunn-elements for X-band oscillator applications

The main purpose of this paper is to develope a procedure for the computer-aided determination of the equivalent circuit of Gunn-elements. In order to determine the equivalent circuit, the Gunne-element is first measured in a test oscillator. Varying the elements of the circuit the calculated frequency and power distribution is adjusted to the measured one by means of an iterative method. The equivalent circuit of Gunn-elements obtained in this way is used for the dimensioning of Gunn-element-oscillators in the X-band in finline technique.     

Zinc oxide nanostructured layers for gas sensing applications

Various kinds of zinc oxide (ZnO) nanostructures, such as columns, pencils, hexagonal pyramids, hexagonal hierarchical structures, as well as smooth and rough films, were grown by pulsed laser deposition using KrF and ArF excimer lasers, without use of any catalyst. ZnO films were deposited at substrate temperatures from 500 to 700°C and oxygen background pressures of 1, 5, 50, and 100 Pa. Quite different morphologies of the deposited films were observed using scanning electron microscopy when different laser wavelengths (248 or 193 nm) were used to ablate the bulk ZnO target. Photoluminescence studies were performed at different temperatures (down to 7 K). The gas sensing properties of the different nanostructures were tested against low concentrations of NO₂. The variation in the photoluminescence emission of the films when exposed to NO₂ was used as transduction mechanism to reveal the presence of the gas. The nanostructured films with higher surface-to-volume ratio and higher total surface available for gas adsorption presented higher responses, detecting NO₂ concentrations down to 3 ppm at room temperature.     

Fabrication of diamond nanorods for gas sensing applications

Diamond nanorods were fabricated for a sensing device by utilizing reactive ion etching in CF₄/O₂ radio frequency plasma. The length of the nanorods has been controlled by the ion etching time. The obtained morphologies were investigated by scanning electron microscopy. The gas sensing properties of the H-terminated diamond-based sensor structures are indicating that we have achieved high sensitivity to detect phosgene gas. Also, our sensor exhibited good selectivity between humid air and phosgene gas if the measurement is conducted at elevated temperatures, such as 140 °C. Furthermore, such sensor response rating could reach as high value as 4344 for the phosgene gas, which was evaluated for the sample consisting of the longest nanorods (up to 200 nm).     

Novel diode laser-based sensors for gas sensing applications

The development of compact spectroscopic gas sensors and their applications to environmental sensing will be described. These sensors employ mid-infrared difference-frequency generation (DFG) in periodically poled lithium niobate (PPLN) crystals pumped by two single-frequency solid state lasers such as diode lasers, diode-pumped solid state, and fiber lasers. Ultrasensitive, highly selective, and real-time measurements of several important atmospheric trace gases, including carbon monoxide, nitrous oxide, carbon dioxide, formaldehyde [correction of formaldehye], and methane, have been demonstrated.     

A nano-scale transducer using a PANDA type ring resonator for gas sensor applications

We present a new system of nano-scale gas sensor using PANDA type ring resonator, whereas the sensing unit is a splitting ring resonator with two and four gaps. The method of finite difference time domain (FDTD) via the computer programming called Opti-wave was used to analyze and simulated all the parameters. The two systems were compared and the simulation result shown that the system of four splitting gaps is better resolution and more linear relationship than two splitting gaps unit. Finally, we found that this system can be used to be a high-precision self-calibration nano-scale gas sensor with in the of resolution of 1 nm.