High-precision Sampling Research Articles

Chemistry and Kinematics in the Solar Neighborhood: Implications for Stellar Populations and for Galaxy Evolution

The immediate Solar neighborhood should be a fair sample of the local Galaxy. However, the chemical abundance distribution of long-lived disk stars very near the Sun contains a factor of five to ten more metal-poor stars, $-1 \simlt {\rm [Fe/H]} \simlt -0.4$ dex, than is consistent with modern star-count models of larger scale Galactic structure. The metallicity distribution of complete samples of long-lived stars has long been recognised as providing unique constraints on the early stages of chemical evolution of the Galaxy, so that one would like to resolve this anomaly. We present a new derivation of the local G-dwarf metallicity distribution, based on the Third Gliese catalog combined with Olsen's (1983) Str\"omgren photometry. Kinematic data for these same stars, as well as for a high-precision sample studied by Edvardsson {\sl et al.} (1993), provide clear evidence that the abundance distribution below [Fe/H]$\sim -0.4$ contains two over-lapping distributions, the thick disk and the thin disk. We achieve a reliable deconvolution of the relative numbers in each population by comparing the local metallicity distribution with a recent determination (Gilmore, Wyse \& Jones 1995) of the metallicity distribution of F/G stars {\sl in situ} some 1500pc from the Sun. The gravitational sieve of the Galactic potential acts on this second sample to segregate the low velocity dispersion, thin-disk, component of the local sample, leaving predominantly the second, higher velocity dispersion component. The combination of these two datasets allows us to determine the source of the local paradox: there is a substantial tail of the thin disk (defined kinematically) metallicity distribution, which extends below ${\rm [Fe/H] \approx -0.4}$dex. This is a robust conclusion, being consistent with the sum of star count, stellar spatial

Mapping of the spectral density function of a C alpha-H alpha bond vector from NMR relaxation rates of a 13C-labelled alpha-carbon in motilin.

The peptide hormone motilin was synthesised with a 13C-enriched alpha-carbon in the leucine at position 10. In aqueous solution, six different relaxation rates were measured for the 13C alpha-H alpha fragment as a function of temperature and with and without the addition of 30% (v/v) of the cosolvent d2-1,1,1,3,3,3-hexafluoro-2-propanol (HFP). The relaxation rates were analysed employing the spectral density mapping technique introduced by Peng and Wagner [(1992) J. Magn. Reson., 98, 308-332] and using the model-free approach by Lipari and Szabo [(1982) J. Am. Chem. Soc., 104, 4546-4570]. The fit to various models of dynamics was also considered. Different procedures to evaluate the overall rotational correlation time were compared. A single exponential time correlation function was found to give a good fit to the measured spectral densities only for motilin in 30% (v/v) HFP at low temperatures, whereas at high temperatures in this solvent, and in D2O at all temperatures, none of the considered models gave an acceptable fit. A new empirical spectral density function was tested and found to accurately fit the experimental spectral density mapping points. The application of spectral density mapping based on NMR relaxation data for a specific 13C-1H vector is shown to be a highly useful method to study biomolecular dynamics. Advantages are high sensitivity, high precision and uniform sampling of the spectral density function over the frequency range.

Accurate Binary Mass Determinations: Goals, Limitations, and Prospects

The state of the art in accurate mass determination for binary stars is reviewed, and the angular sizes and their errors are computed for a typical system from the existing high-precision sample. It appears that sub-μas (microarcsecond) absolute astrometry will be needed in order to improve the accuracy substantially by astrometry alone. The types of system, and the kinds of data, where precision astrometry appears most promising are outlined. Finally, astrophysical applications of such accurate stellar masses, and the auxiliary data required in them, are briefly reviewed.

FERMI-a new generation of electronic modules for large data acquisition arrays required by high energy physics

The FERMI, Front End Readout MIcrosystem, is representative for a new generation of data acquisition modules which utilizes modern design techniques to achieve high acquisition rates together with intelligent on-line data processing. FERMI is being designed to satisfy the extreme requirements set by calorimeters in the next generation of particle physics detectors. Such detectors are currently being designed for the future LHC accelerator at CERN in Switzerland. The calorimeters demand frequent (40 MHz or 80 MHz, if sampled between bunch crossings) high precision sampling of a large number of input channels (about 5.10/sup 5/). Each FERMI module serves 9 channels from which samples are AD-converted, corrected and temporarily stored in a local memory. The data is also merged into a trigger sum, which is processed by digital filters to determine the arrival time and amplitude of incoming pulses. Such data is then fed to a first-level trigger processor which screens irrelevant information. Only data that may contain useful information is kept for further analysis. Arrays of 50000 FERMIs constitute a formidable processing system when considering its total computational power and storage capacity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurement of two-dimensional strain distribution by speckle correlation

This paper reports a parametrically amplified MEMS rate gyroscope. A practical parametric excitation scheme implemented using Digital Signal Processing (DSP) has been developed to enable either amplification of the primary mode of the gyroscope or amplification of the response to the applied angular velocity. The primary objective of this work is to improve the scale-factor and the signal to noise performance of the gyroscope. Parametric amplification of the primary mode of the gyroscope is achieved by frequency tracking and regulation of the amplitudes of the harmonic forcing and parametric excitation to maintain a desired parametric gain by closed loop PID control. Stable parametric amplification of the primary mode by a factor of 20 is demonstrated experimentally. This has important benefits regarding the minimisation of electrical feedthrough of the drive signal to the sense electrodes of the secondary mode. By taking advantage of the phase dependence of parametric amplification and the orthogonality of the Coriolis force and quadrature forcing, the response to the applied angular velocity may be parametrically amplified by applying excitation of a particular phase directly to the sensing mode. The major advantage of parametric amplification applied to MEMS gyroscopes is that it can mechanically amplify the Coriolis response before being picked off electrically. This is particularly advantageous for sensors where electronic noise is the major noise contributor. In this case parametric amplification can significantly improve the signal to noise ratio of the secondary mode by an amount approximately equal to the parametric amplification. Preliminary rate table tests performed in open loop demonstrate a magnification of the signal to noise ratio of the secondary mode by a factor of 9.5 and the scale-factor by 11. The excitation and control scheme have been implemented digitally using a DSP development board enabling very high sampling precision and execution speed necessary for gyroscopic applications.

Ion microprobe system combined with scanning electron microscope for high precision aiming

An ion microprobe system with high precision for target alignment has been realized by combining a compact scanning electron microscope (SEM) column with a target chamber. The target alignment is done first by imaging sample features with a scanning electron microscope (SEM) and then fine alignment of the sample position with respect to the incident ion beam is accomplished by comparing the secondary electron images of a Si test sample produced by the SEM beam and the ion microbeam. A Si test sample, with a specially designed relief pattern, has been used for both measuring the beam size and for determining the exact incident site of the ion beam on the target. Precision of aiming at present is about 5 μm which is limited mainly by the mechanical precision of the SEM sample holder. A beam spot size of 1.9 × 1.7 μm (FWHM) for 3 MeV He + beam has been achieved. Use of a high precision sample manipulator affords the prospect of an ion alignment precision of about 2 μm.

Potentiometric and conductometric determination of ammonium by gas-diffusion flow injection analysis

Considerable enhancement of selectivity in the potentiometric and conductometric determination of ammonium is provided by gas-diffusion separation in flow injection analysis. Ammonium and potassium selective liquid membrane electrodes can be used for determinations in the concentration range 10−7–10−2 mol/l with high precision and fast sample throughput. No interferences are encountered in the presence of ionic species and molecules that likely adsorb when the sensors are in direct contact with the sample. The selectivity over volatile amines is enhanced due to kinetic discrimination. Conductometric detection is shown to be as sensitive as the potentiometric detection. A major advantage, however, is the linear rather than logarithmic relationship between concentration and conductivity.

Performance evaluation of a new audio-frequency power bridge

Several techniques for measuring active and reactive power in the 50-Hz to 20-kHz frequency range are described. These approaches were developed to evaluate a new high-accuracy, audio-frequency power bridge that is based on AC voltage and impedance measurements. The results indicate that its uncertainties are within the expected +or-200 p.p.m. for active power. The bridge and a high-precision sampling wattmeter constructed using two sampling digital voltmeters are described. A dual-channel digitally synthesized source was used to verify measurements at zero power factor. >

Neutron diffraction by laser-generated volume phase gratings

Cold neutrons are diffracted by thick phase gratings which have been produced by light-optical holography in poly-(methyl methacrylate) (PMMA). The neutron diffraction efficiency is investigated in the Laue case as a function of the angle of incidence by rocking the sample. The dynamical theory of neutron diffraction allows to relate the measured diffraction efficiency to the modulation amplitude of the neutron-optical refractive index. The absence of higher order diffraction peaks proves that this modulation is sinusoidal. Further experimental parameters are shown to influence the diffraction in accordance with the dynamical theory: the wavelength of neutrons, the sample thickness, and the grating period. Laser diffraction experiments allow us to give upper limits for the uniformity of the grating constant throughout the sample volume. The gratings show properties which are promising for the fabrication of high-precision control samples for cold and very cold neutron spectrometers, for the construction of neutron-optical instruments, and the possibility to measure photoinduced changes of neutron-optical potentials.

High-precision sampling of sub-nanograms, low-parts-per-billion solutes from liquids using the dynamic solvent effect

The quantitative precision of dynamic solvent-effect sampling from solvent specimens is reported. For sub-nanogram amounts of a range of solutes at a concetration of 5:109 the coefficients of variations of peak areas, peak percentage areas and peak-area ratios are consistently below 10%. The dynamic solvent effect allows high-precision sampling of much smaller amounts of solute than do alternative sampling methods.

High-precision sampling of trace gas-borne volatiles by the dynamic solvent effect with a comparative review of alternative techniques

The precise determination of traces of organic volatiles is particularly challenging in semiochemistry and clinical chemistry, where specimen sizes are intrinsically limited and amounts of trace components correspondingly very small. This demands a sampling technique that is fully compatible with the ability of capillary columns and gas chromatographic detectors to separate and quantify nanogram and sub-nanogram amounts from complex mixtures. The quantitative precision of dynamic solvent-effect sampling of low parts per billion (10 9) aqueous carbonyl compounds, high ppb and low parts per million aqueous phenols, low ppb and high parts per trillion (10 12) airborne hydrocarbons and the volatiles from wine, human urine and a slow-release pesticide was tested with specimen sizes that yielded amounts of volatiles down to the sub-nanogram level. Provided that sources of variability, such as temperature changes, adsorption on containers, incomplete peak resolution and changes in the specimens themselves, were adequately controlled, dynamic solvent-effect sampling consistently provided coefficients of variation in peak areas, peak percentage areas and peak-area ratios of less than 10% at nanogram and sub-nanogram levels. The literature was surveyed for data on the performance of other sampling systems. None of them have been demonstrated to match the precision of the dynamic solvent effect with such small amounts from such a wide range of materials.

High-precision sampling for Brillouin-zone integration in metals.

We present a sampling method for Brillouin-zone integration in metals which converges exponentially with the number of sampling points, without the loss of precision of normal broadening techniques. The scheme is based on smooth approximants to the \ensuremath{\delta} and step functions which are constructed to give the exact result when integrating polynomials of a prescribed degree. In applications to the simple-cubic tight-binding band as well as to band structures of simple and transition metals, we demonstrate significant improvement over existing methods. The method promises general applicability in the fields of total-energy calculations and many-body physics.

High-performance liquid affinity chromatography: rapid immunoanalysis of transferrin in serum.

We describe a new method for quantitatively measuring substances of clinical interest by high-performance liquid affinity chromatography (HPLAC). As a model system we selected analysis for transferrin in human serum with immobilized antibodies in a high-performance liquid chromatographic system. SelectiSpher-10 Activated Tresyl columns (5 or 10 x 0.5 cm) were used for in situ coupling of polyclonal antibodies to transferrin. The amount of transferrin eluted was determined by integrating the eluted peak at 280 nm. The whole analytical procedure--including injection of sample, washing, elution, and analysis of data--takes only 7 min. We characterized the HPLAC system for analysis of transferrin in several ways: intra-assay CV approximately 3%; inter-assay CV 2-9%; linear response up to 1 mg/mL column volume; detection limit approximately 3 micrograms; analytical recovery 98% +/- 2%; purity of eluted sample greater than 95% (SDS-PAGE). The HPLAC method was compared with "rocket" immunoelectrophoresis, a commonly used method of analysis for transferrin, and there was excellent correlation between the two methods (r = 0.96, n = 60). Benefits of this HPLAC technique include high precision, rapid analysis, and simplified sample handling.

Acoustical absorption spectroscopy of liquids between 0.15 and 3000 MHz. I. High resolution ultrasonic resonator method

A technique is described to determine the sound absorption coefficient of liquids by means of a sensitive resonator method. Details of the construction of high-precision sample cells are shown and the electronic circuit for computer-controlled measurements is presented. Also discussed are various possible sources of experimental errors and appropriate data recording and evaluation procedures. Results are given to illustrate the accuracy of this measurement technique.

Novel double-isotope technique for enzymatic assay of catecholamines, permitting high precision, sensitivity and plasma sample capacity.

1. A novel use of a double-isotope method is described which allows radioenzymatic assays to combine precision and sensitivity. 2. In the catechol O-methyltransferase assay separate portions of each plasma sample are incubated with either S-[3H]- or S-[14C]-adenosyl-L-methionine. Standards of noradrenaline and adrenaline are added to the latter portions and are thus converted into standards of [14C]metadrenalines. These are added to the 3H-labelled portions after the incubation, where they function as tracers. 3. The final recovery of 14C radioactivity corrects for (a) the efficiency of methylation in the plasma sample concerned and (b) the recovery of metadrenalines during the extraction procedures. 4. The 3H/14C ratio is constant in each assay for a given catecholamine concentration and is determined for samples to which standards of noradrenaline and adrenaline are added to the 3H- (as well as the 14C-) labelled portions before the initial incubation. 5. The sensitivity of the assay is increased by using high specific radioactivity S-[3H]adenosyl-L-methionine (60--85 Ci/mmol), and low backgrounds are maintained by catecholamine depletion in vivo in the rats use for enzyme preparation. 6. Both catecholamines (1.5 pg/ml; 10 pmol/l) may be detected; the coefficients of variation are 3.0 and 3.2% for noradrenaline and adrenaline respectively (intra-assay) and 4.6 and 5.0% (inter-assay).

High-performance liquid chromatographic analyses of the antihypertensive drug cartopril

High-performance liquid chromatographic systems have been developed to separate and quantitate captopril. The presence of interfering excipients in various formulations necessitated the development of three assays, each with distinctly different columns and mobile phases. All work well for bulk material, providing short analysis time, high precision, and rapid sample preparation, demonstrating that there is not necessarily one, best, high-performance liquid chromatographic system. The advantages and shortcomings of the ion-exchange, amino and octadecyclsilane system are evaluated and one of them is selected as optimum for bulk and tablet analysis.

Advances in high precision sample positioning stages for electron-beam microfabrication and metrology

An improved computer controlled X–Y stage has been built for electron-beam microfabrication and metrology. The stage servo drives and the laser stage position sensors are mounted directly to the stage vacuum chamber to provide maximum rigidity. An ’’L’’ shaped chromium carbide mirror provides a reference with 1/4 arc-s accuracy for the stage position sensing laser, while allowing the sample to be in the plane of the laser beams to eliminate position sensing errors due to pitch and yaw of the stage. A reference chip is mounted on the stage in the plane of the sample to aid in initial focus and registration. For precision manual control of the stage a digital joystick is used. Nonlinear shaping networks on a standard linear taper joystick enable the operator to easily position the stage to 0.01 μm and still be able to move at full slew speed (1 cm/s). For each axis, V–F converters are used to convert the analog output of the shaping network to a digital pulse train which feeds a 24 bit closed loop servosystem. A digital tach is used for damping. Rate feedback is derived from the laser interferometer system rather than the conventional generator coupled to the servomotor. High torque motors are used for improved acceleration and dynamic braking. Servomotor-to-stage-drive coupling incorporates a friction lead screw to eliminate backlash. Under computer control, repeatability of positioning has been determined to be 0.01 μm. Accuracy is 0.01 μm/cm plus 0.005 μm/cm of stage travel (laser interferometer error).

Optimization of chromatographic separations by computer control

A system for optimizing gas chromatographic separations by computer control in real time is described. The GC-CPU interface controls the high precision sampling valve, temperature controller, flow controller, programmable gain amplifier, and time base. Algorithms for data acquisition, data reduction, and control are outlined. The criteria for optimization of the experimental conditions are based on peak symmetry, resolution, and relative retention. This approach is compared to other modes of control such as precolumn techniques, serial column switching, recycling columns, and library file searching.