Standard Mode Of Operation Research Articles

Macromolecular crystallographic results obtained using a 2048×2048 CCD detector at CHESS

We present results of macromolecular crystallographic experiments performed at the Cornell High Energy Synchrotron Source (CHESS) with a new CCD-based detector. This detector, installed in January 1995, complements a 1024×1024 CCD detector that has been in continuous operation at CHESS since December 1993. The new detector is based on a 4-port, 2048×2048 pixel CCD that is directly coupled to a Gd2O2S:Tb phosphor by a 3:1 tapered fiber optic. The active area of the phosphor is a square 82 mm on an edge. The readout time is 7 seconds. In the standard mode of operation, the pixel size at the active area is 41 μm on the edge leading to the capability of resolving approximately 200 orders of diffraction across the detector face. The detector also operates in a 1024×1024 mode in which the pixel size is electronically increased by a factor of 4 in area resulting in smaller data files and faster detector readout but at the expense of spatial resolution. Most of the data that has been collected by this detector has been collected in this mode. Dozens of data sets have been collected by many experimenters using this detector at CHESS during the four month period from its installation until the start of the six-month down period of the storage ring. The capabilities of the detector will be illustrated with results from various crystallographic measurements including experiments in which the recorded diffraction patterns extend in resolution as far as 1 Å. The results demonstrate that this detector is capable of collecting data of quality at least equal to that of imaging plates but, in many circumstances, with much greater beamline efficiency.

Mapping viscoelasticity, (specific) adhesion and near-field fluorescence of cellular structures with scanning probe microscopy

One of the major features of scanning probe microscopy is the ability to produce high-resolution images in air and in liquid. This makes these microscopes potentially very useful for the study of biological materials. Indeed the number of reports that use these microscopes, especially the atomic force microscope (AFM), has increased exponentially in the past decade. However, in order to become a routine apparatus that is able to image live processes at a scale of a few nanometers, the instrumentation of the AFM has to be improved. First of all, under normal operation, the movement of the tip across the surface of fragile biological structures such as cell membranes, often results in movement or even destruction of the object. Secondly, the lack of specificity of the AFM makes it difficult to identify the observed structures. Other problems include the low imaging speed and problems associated with the tip-sample convolution. Here we will report on attempts to improve the first two points: sample destruction and specificity.It has become clear recently that for operation in air the so-called tapping mode AFM is much more gentle for the sample than the standard operation mode.

Plasma-surface interactions in the Alcator C-Mod tokamak

Alcator C-Mod is a high-field tokamak with which experiments were initiated in April 1993. The divertor and the first-wall have plasma-facing surfaces of molybdenum. The divertor has a configuration which is closed in comparison to other, currently operating tokamaks. The combination of divertor geometry and high field (density) make Alcator C-Mod an ideal experiment to investigate dissipative (radiative/CX) divertor scenarios. Single-null divertor operation has become the standard mode of operation. Relatively clean plasmas ( Z eff ≤ 1.3) are obtained with short periods of baking and electron cyclotron discharge cleaning only. Impurity source rates and screening have been investigated with an extensive set of wavelength-filtered diode arrays and spectrographs. Carbon and oxygen and molybdenum dominate the impurity levels. The molybdenum source from the divertor proper is negligible.

Sediment Feed and Recirculating Flumes: Fundamental Difference

Two standard modes of laboratory sediment transport flume operation are sediment‐feed and recirculating. In the case of uniform sediment, the final equilibriums achieved in the two modes are equivalent and independent of initial conditions, even though the specified flow and sediment constraints differ. When the sediment consists of a mixture of sizes, however, this symmetry breaks down. In a sediment‐feed flume, both the feed rate and size distribution are specified by the user, and must be identical to those of the bed load at final equilibrium. The final state thus becomes independent of initial conditions. In a recirculating flume, however, the equilibrium size distribution of neither the bed load nor the bed surface material can be specified in advance. As a result, the final state depends on the initial conditions and can include the possibility of partial transport. The equilibriums themselves are equivalent in that they obey the same laws of flow and sediment transport. Their a‐priori predictability, however, differs due to the difference in governing constraints. When fractional transport is scaled by the bulk size distribution, the two flume modes may produce very different transport relations, even for the same sediment. A consistent approach requires that the transport be scaled by the size distribution of the bed surface.

Integrating mode for an optically addressed spatial light modulator

We describe the integrating-mode operation of an optically addressed spatial light modulator that incorporates a ferroelectric liquid-crystal light-modulating layer and an amorphous-silicon photodiode. This mode of operation uses a higher drive frequency and produces a readout response that extends over several driving periods, thereby permitting cw operation. The response characteristics of the device can be adjusted by varying the amplitude and offset of the applied voltage. Spatial resolution of 40 line pairs/mm, response times of 1 ms, and contrast ratios of 30:1 were achieved in this mode. We compare the integrating mode of operation with our standard reset mode of operation, whereby the electrical driving frequency is sufficiently low that the liquid crystal can respond fully to the voltage level during each part of the drive, and the device is reset fully to its off state during the forward-bias part of each electrical bias period.

The gradient tensor of potential field anomalies: Some implications on data collection and data processing of maps

The full gradient tensor is presently not measured routinely onboard airplanes or on land. This paper describes some improvements that can be made in strategies of data collection and in processing of potential field maps if such tensor measurements were available. We suggest that, in addition to producing for example standard total field anomaly maps, the invariants of the tensor be mapped. Strikes of magnetic or gravimetric structures may be determined from minimizing the power in the first row and column of the tensor. Invariants can be looked upon as nonlinear filters enhancing sources with big volumes. Their lateral resolution is superior to that of the field proper and, for a given resolution, the flight altitude and separation between flight lines can be increased compared with the standard mode of operation. In airborne surveys the distance between flight lines is normally much larger than the height above the ground. This may introduce severe aliasing effects in the direction perpendicular to the flight lines. By increasing the flight altitude, aliasing effects are reduced at the expense of lateral resolution which, however, may be improved by mapping the tensor invariants in addition to the magnetic field. The estimated gradient tensor from total field magnetic data over the Siljan impact region shows that the magnetic properties of the area are very nonuniform even from a height of 430 m above the topography. The nonlinear filters discriminate major anomalies into separate units.

Kinematic GPS Land Survey—Description of Operational Test and Results

A kinematic GPS (Global Positioning System) survey was performed by the National Geodetic Survey to determine the feasibility of using the method operationally on some geodetic surveying projects. The method of the experiment is described, and results from two GPS data reduction packages are presented along with results of a terrestrial survey performed on the same network of stations. Operationally oriented discussions of the kinematic method., project planning and execution, and suggestions for future kinematic software and hardware are included. The antenna swap method of determining integer biases is described. The survey demonstrates that with little modification of equipment or software, it is possible to implement kinematic surveying as a standard mode of operation on many NGS (National Geodetic Survey) projects. The results of the survey indicate that with station occupation periods of 2 min the repeatability of base line vector components determined by kinematic methods will be subcentimeter.

Longitudinally polarized proton beams at TRIUMF

Beam line 4B at TRIUMF has been modified to allow production of polarized proton beams of all polarization components (normal, sideways and longitudinal). This was achieved by the installation of two 2.4 T m superconducting solenoids in the cyclotron vault section of the beam line. It was also required to be able to rotate one vault quadrupole. It was found that for longitudinal polarization in beam line 4B the twister could no longer be operated as a unit section. The standard achromatic and dispersed modes of operation of beam lines 4A and 4B are still available.

The conditions for Lorenz chaos in an optically-pumped far-infrared laser

The conditions for Lorenz chaos in cw optically pumped far-infrared (FIR) lasers are more stringent than those derived in two level systems due to the pump laser induced coherence. We list a set of six conditions which should be fulfilled in order to observe Lorenz chaos. The main new requirement is a fast relaxation of the off-diagonal elements involving the ground rotational molecular level. We propose the use of a chaotically emitting pump laser in order to avoid the induced coherence effects. By comparison with the standard mode of operation, useful insight into the coherent dynamics of optically pumped lasers could be gained.

Beyond bathymetry: Mapping acoustic backscattering from the deep seafloor with Sea Beam

In its standard mode of operation, the multibeam echo sounder Sea Beam produces high resolution bathymetric contour charts of the seafloor surveyed. However, additional information about the nature of the seafloor can be extracted from the structure of the echo signals received by the system. Such signals have been recorded digitally over a variety of seafloor environments for which independent observations from bottom photographs or sidescan sonars were available. An attempt is made to relate the statistical properties of the bottom-backscattered sound field to the independently observed geological characteristics of the seafloor surveyed. Acoustic boundary mapping over flat areas is achieved by following trend changes in the acoustic data both along and across track. Such changes in the acoustics are found to correlate with changes in bottom type or roughness structure. The overall energy level of a partial angular-dependence function of backscattering appears to depend strongly on bottom type, whereas the shape of the function does not. Clues to the roughness structure of the bottom are obtained by relating the shape of the probability density function of normal-incidence echo envelopes to the degree of coherence in the backscattered acoustic field.

Pondering pandering

The purpose of this paper is to examine the pandering activities of pimps and to formulate a critique of the concept of pandering. First, popular perceptions of the phenomenon are described in terms of a case story. Information on preferred recruitment sites (e.g., bus terminals) and standard modes of operation (talk, drugs, and violence) is provided. Next, the results of two exploratory studies are reported. Police perspectives are revealed through a survey of Port Authority police officers. An attempt to generate pandering is carried out by means of participant observation. These studies yield contradictory information, and an attempt to institute a compromise moves the analysis to the question of control, specifically whether prostitutes are victims or volunteers. Upon analysis, the relationships that previously constituted the process of pandering and the activities that usually characterized the pimp's role are reversed. Finally, perspectives on the social construction of the pandering reality are summarized.

Rotating conventional gamma camera single-photon tomographic system: physical characterization.

A whole-body single-photon emission computed tomography system has been evaluated in terms of its physical performance. It consists of a standard GE 400 T maxi camera rotating on a ring stand, coupled to an Informatek Simis 3 computer system. In its standard mode of operation, 64 or 128 successive views of 64 X 64 or 128 X 64 matrices are collected at regular angular samples. The reconstruction of up to 64 possible adjacent transverse sections, sorted into coronal, sagittal, and oblique sections, is obtained by filtered backprojection. A conventional parallel-hole collimator is used. The uniformity of the camera field of view is corrected by the GE hardware module. The resolution in the transverse plane is typically of 15.5 mm in a 20 cm Lucite phantom, and independent of radial distance. The physical slice thickness is 19 mm (full width at half maximum of the longitudinal response using a point source) with only slight variations along the diameter of the image. The sensitivity is approximately 7,000 cps mCi-1 as measured using a 99m Tc thin source, enabling images of reasonable signal-to-noise ratio to be obtained in 10 min. The effect of the energy window, the number of angular samples, and the linear sampling modes on the transverse resolution and contrast is measured and discussed.

Progress in Radio-Echo Sounding Theory

AbstractThe inverse problem of radio-echo sounding consists in the reconstruction of subglacial relief from the known radio-echo profile, and the path, and speed of the aircraft. The present work shows that in the geometrical optical approach the solution of the inverse problem for a homogeneous, two-dimensional object (valley glacier) exists, and there is a unique solution. An algorithm for interpretation of the experimental data is suggested. It may be considered as the generalization of Harrison’s transformations for any surfaces. paths, and speed.The direct problem of radio-echo sounding consists in the reconstruction of radio-echo profile from the known surface and subsurface relief, path, and aircraft speed. The analysis of traces in the standard radio-echo sounding mode of operation reveals the possibility of introducing a three-index trace classification {K, sign S’(o), K+} where K is the number of real roots characteristic of the equations, K+ the number of positive roots, and S’(o) the position derivative, the argument being equal to zero. The form {o, — o} is optimal for the precision of the calculation of the reflected surface coordinates, as well as for the simplicity of the interpreted picture. By a special choice of the altitude of flight, any form of any surface can be brought to {o, —o}. The decrease in beam width is equivalent to the diminution of roots of the characteristic equations. For a pencil beam the trace degenerates into a point.The attenuation of the reflected signal depends on the glacier geometry, the dielectric parameters of the medium, the altitude and the course of the aircraft, as well as statistical characteristics of the mutual orientation of the interfaces and aerials. For the description of the energetics of radio-echo sounding, equivalent reflecting surfaces are suggested. These surfaces correspond to the Harrison’s equivalent reflecting surface. Exact formulae for the power of coherent and incoherent components of the reflected signal are obtained. Components of the full attenuation such as absorption, depolarization, and spherical divergence, are investigated with respect to refraction and focusing effects.

Progress in Radio-Echo Sounding Theory

Abstract The inverse problem of radio-echo sounding consists in the reconstruction of subglacial relief from the known radio-echo profile, and the path, and speed of the aircraft. The present work shows that in the geometrical optical approach the solution of the inverse problem for a homogeneous, two-dimensional object (valley glacier) exists, and there is a unique solution. An algorithm for interpretation of the experimental data is suggested. It may be considered as the generalization of Harrison’s transformations for any surfaces. paths, and speed. The direct problem of radio-echo sounding consists in the reconstruction of radio-echo profile from the known surface and subsurface relief, path, and aircraft speed. The analysis of traces in the standard radio-echo sounding mode of operation reveals the possibility of introducing a three-index trace classification {K, sign S’(o), K+} where K is the number of real roots characteristic of the equations, K+ the number of positive roots, and S’(o) the position derivative, the argument being equal to zero. The form {o, — o} is optimal for the precision of the calculation of the reflected surface coordinates, as well as for the simplicity of the interpreted picture. By a special choice of the altitude of flight, any form of any surface can be brought to {o, —o}. The decrease in beam width is equivalent to the diminution of roots of the characteristic equations. For a pencil beam the trace degenerates into a point. The attenuation of the reflected signal depends on the glacier geometry, the dielectric parameters of the medium, the altitude and the course of the aircraft, as well as statistical characteristics of the mutual orientation of the interfaces and aerials. For the description of the energetics of radio-echo sounding, equivalent reflecting surfaces are suggested. These surfaces correspond to the Harrison’s equivalent reflecting surface. Exact formulae for the power of coherent and incoherent components of the reflected signal are obtained. Components of the full attenuation such as absorption, depolarization, and spherical divergence, are investigated with respect to refraction and focusing effects.

Adaptation of a Recording Spectropolarimeter to Measure Circular Dichroism

SUMMARYMany of the optical, electrical, and mechanical components andsystems of a recording spectropolarimeter may be used in adapting the spectropolarimeter to measure and record circular dichroism. This article describes the construction and performance characteristics of an accessory for the measurement of circular dichroism in the 6000-1850 A region on a commercially available recording spectropolarimeter, the Cary Instruments Model 60. The accessory employs an improved version of the electro-optic modulator technique. It consists of four units which are easily coupled to the spectropolarimeter. Furthermore, conversion of the spectropolarimeter to the standard mode of operation is readily achievable.

Characteristics of a λ/2 Kerr Cell Ruby Oscillator for Use as an Optical Radar (Lidar)

A Q-switched ruby laser has been developed that is useful as an optical radar for clear air turbulence detection. The output is a single clean pulse of 35 MW, free of noise sources such as spontaneous emission, superradiance, and after-pulsing. A comparison is made with the standard quarter-wave mode of operation.