Physical Probe Research Articles

Limits of SEM resolution

Over the past decade the achievable resolution of the scanning electron microscope (SEM) in secondary electron (SE) imaging mode has improved by about one order of magnitude. In fact, instruments capable of demonstrating a resolution of one nanometer and exhibiting a probe size of less than 0.6nm are now available. Continued improvements in electron-optics, electron sources, and in electronic and mechanical stability promise even smaller probe sizes that still contain adequate current for imaging. It is therefore relevant to consider what resolution might ultimately be achievable with an SEM in SE mode.The contrast detail in an SE image depends on two factors, the generation of secondaries, and their subsequent escape from the specimen. Changes in either, or both, of these factors will change the number of secondaries collected, and the spatial scale over which this change is accomplished will set the effective resolution of the image (assuming that the physical probe size is small enough to be neglected).

Physical and chemical probes of metallic clusters

Two different approaches for studying the electronic structure of clusters are presented. The physical probe uses the photoexcitation of size selected alkali-atom clusters. Giant resonances govern the absorption cross-section. It is due to the collective excitation of delocalized valence electrons. The behavior of the resonance up to large sizes, 900-atom clusters for potassium and 1500-atom clusters for lithium puts into evidence the failure of the jellium model for lithium. The chemical approach makes use of the nucleation process in the presence of oxygen. From the analysis of mass spectra of oxidized products, informations are gained on the valence of metallic atom in the cluster oxide. The method is applied to europium and thulium clusters. A comparison is done with the simple case of alkali clusters.

E-beam probe potential diagnostic in spherical electrostatic-inertial plasma confinement (SEIC) (abstract)

A new e-beam probe is developed to study the potential structure inside a SEIC device [G. H. Miley et al., Fusion Technol. 19, 840 (1991)]. The device has a spherical grid negatively biased inside a spherical vacuum chamber. Ions oscillate through the highly transparent grid, forming a single potential well inside the cathode. The potential in turn attracts electrons from ionization of background gas. The measurement of this complex potential profile is the objective of this work. The e-beam probe offers advantages over the e-emitting probes and the laser heterodyne method. It minimizes perturbations (versus a physical probe) and detects smaller charge density variations than possible with laser techniques. The present e-beam probe utilizes a higher voltage and a modified focus compared to the earlier version used by Swanson [Swanson et al., Phys. Fluids 16, 1939 (1973)]. The characteristic e-beam deflection patterns observed are compared to predictions from an impulse approximation model.

The use of spin labels in looking at subtle conformational changes in blood coagulation proteins

Abstract

Review of physical diagnostic techniques in medicine and biology: technical progress and future requirements

The paper aims to introduce the reader to the wide array of diagnostic devices, based on physical processes, which are now available or under development, and also to indicate aspects which require further technical development or even a new approach to design and construction. Recent technological progress has led to the availability in developed countries of many diagnostic techniques, e.g. X-ray and NMR imaging, positron emission imaging, thermography. The technical basis of a number of these methods is described with emphasis on the nature of the information which may be obtained. Some of these techniques do not involve any ionising radiation dose. This condition offers the possibility of repeated investigations of the same patient in order to follow the progress of disease and of treatment. It also suggests new possibilities for mass screening in order to detect people at risk. In some cases, engineering development has taken place in advance of scientific understanding of the response of biological tissue to the physical probe, and this has delayed full realisation of the potential of the method. Many of the newest devices involve high capital and running costs, and require well-qualified technical support. The need for low cost, robust devices is discussed with particular reference to the UK Health Service and the needs of developing countries.

Planar imaging of a turbulent methane jet

Introduction I N this Note, concentration measurements are reported for a round methane jet discharging into air at moderate Reynolds number. The primary objective of this study was to compare concentrations determined by two independent methods, planar digital imaging and gas sampling (physical probe). Since elastic light scattering from small seed particles was used in the optical determination of gas concentration (i.e., marker nephelometry), the experiment also provided information on the adequacy of marker nephelometry at a relatively low Reynolds number.

Progress toward a metal-base transistor

Interest has been revived in the silicon metal-base transistor because of significant progress in growing thin, single-crystal metal films on silicon. The unique properties of silicides are described and the possibility of attaining ballistic transport in silicides is discussed. The use of the metal-base transistor as a physical probe is considered.

A scaling law: How an attractor's volume depends on noise level

We investigate the meaning of the dimension of a strange attractor for systems with noise. More specifically, we investigate the effect of adding noise of magnitude ε to a deterministic system with D degrees of freedom. If the attractor has dimension d and d < D, then its volume is zero. The addition of noise may be an important physical probe for experimental situations, useful for determining how much of the observed phenomena in a system is due to noise already present. When the noise is added, the attractor A ε has positive volume. We conjecture that the generalized volume of A ε is proportional to ε D − d for ε near 0 and show this relationship is valid in several cases. For chaotic attractors there are a variety of ways of defining d and the generalized volume definition must be chosen accordingly.

The stoichiometry of photorespiration during C 3-photosynthesis is not fixed: Evidence from combined physical and stereochemical methods

The stoichiometry of photorespiration, S, is defined as the fraction of glycolate carbon photorespired. It is postulated that under steady-state conditions there are two determinants of the ratio of photorespiration to net photosynthesis: (1) the partitioning of ribulose bisphosphate between oxidation and carboxylation, and (2) the partitioning of glycolate between reactions leading to complete oxidation to CO 2 ( S = 100%) and those yielding CO 2 plus serine ( S = 25%). S may be calculated using two independent probes of the system. The physical probe, using an infrared gas analyzer, measured photorespiration and net photosynthesis, and hence their ratio PR NPS = p n ( phys) . The metabolic probe employed tracer (3 R)- d-[3- 3H 1,3- 14C]glyceric acid to determine r, the fraction of 3H retained in the triose phosphates leaving the chloroplasts. It is deduced from the postulated model that S = p n ( phys)·r (1 − r) . Experiments have been performed with illuminated tobacco leaf discs (inverted) under varying concentrations of O 2 and CO 2. Increasing O 2 at constant CO 2 increased p n(phys) and decreased r, whereas increasing CO 2 at constant O 2 had the opposite effect. S more than doubled at 32 °C on going from 16 to 40% O 2 (340 μl CO 2/liter) and decreased 40% on going from 200 to 700 μl CO 2/liter (21% O 2). For discs in normal air S was somewhat greater than 27%. It is suggested that net photosynthesis, and therefore crop yields, could be increased by selecting for crop plants with reduced photorespiration stoichiometry.

1H-Nuclear magnetic resonance of intercalators and rGCA: A potential mutagenicity probe

Variable temperature 1H-nuclear magnetic resonance (NMR) has been used to study the interaction of the RNA trimer, GpCpA, with the intercalators ethidium bromide and the acridine derivatives; proflavin, 9-amino-acridine, acridine orange, acridine yellow and acriflavin. The complexes formed were studied at nucleic acid to drug ratios of 1:1 and 5:1, the latter being useful in defining the effects of structural variation in the acridine series and in determining the site of intercalation. All the intercalators greatly stabilized the oligonucleotide duplex, the average melting temperature ( T m ) increasing by up to 30°C. Significant changes in individual T m s and chemical shifts were observed for all the GpCpA protons. 9-Amino-acridine and acriflavin did not stabilize the GpCpA duplex as substantially as the other acridine derivatives. It is suggested that this intercalator: GpCpA system, and its associated NMR-derived T m , is a useful physical probe for potential mutagens.

Fluorescent probe analysis of erythrocyte membranes in myotonic dystrophy.

Previous electron spin resonance studies in myotonic muscular dystrophy (MyMD) have suggested that an increased cell surface membrane "fluidity" might underlie the widespread abnormalities in this disorder. We attempted to confirm and expand those findings by using another physical probe technique: fluorescence polarization spectroscopy. Spectral characteristics and rotational relaxation rates of four hydrophobic fluorescent probes were monitored in control and MyMD erythrocyte membrane ghosts. Structural unrelated probes were used to minimize the possibility that an alteration in physical properties in a restricted membrane microdomain would pass undetected. All probes were studied between 5 degrees C and 40 degrees C in each preparation to quantitate temperature-dependent changes. We failed to confirm the abnormality in apparent membrane fluidity previously reported in MyMD.

Chromium (III) thiamin diphosphate: a new probe of enzyme coenzyme--metal ion binding. Interaction with wheat germ pyruvate decarboxylase.

Chromium (III) thiamin diphosphate (CrTDP) is a substitutionally inert complex which is a physical and kinetic probe of the binding mode of metal ion and coenzyme in thiamin diphosphate (TDP) dependent enzymes. CrTDP is prepared by reaction of aquated Cr (III) and TDP and purifed by ion-exchange chromatography. CrTDP binds to the apoenzyme of wheat germ pyruvate decarboxylase, giving an inactive holoenzyme. Chromium (III) ion binds to the apoenzyme in a manner that suggests, in light of the results with CrTDP, that there are two metal ion binding sites. Extension of the use of CrTDP to other enzymes can give specific information about binding and can introduce an active site reporter group

Rabbit brain purine nucleoside phosphorylase: Physical and chemical properties. Inhibition studies with aminopterin, folic acid and structurally related compounds

Rabbit brain purine nucleoside phosphorylase used in this study was purified 6000-fold to apparent homogeneity and a specific activity or 50 μmol min −1 mg −1 protein. A molecular weight of 70.000 daltons was determined for the native enzyme by gel filtration on Sephadex. Electrophoresis on polyacrylamide gel, in presence of sodium dodecyl sulfate, gave a subunit molecular weight of 34,500 daltons, suggesting that the enzyme is dimeric with, probably, identical subunits. The relationship of the structure of certain biologically active substances to their inhibitory action on the enzyme was examined. Folic acid and the compound d,l-6-methyl 5,6,7,8-tetrahydropterine, with similar substituents on their primary ring structure, were competitive inhibitors of the enzyme. The inhibition constants calculated were 3.37 × 10 −5 M for folic acid and 3.80 × 10 −5 m for d,l-6-methyl 5,6,7,8-tetrahydropterine. Aminopterin and the purine analog 8-aza-2,6-diaminopurine, with similar substituents on their primary ring structure, were noncompetitive inhibitors of the enzyme. Their respective inhibition constants were 1.50 × 10 −4 and 1.95 × 10 −4 m. Erythro-9-(2-hydroxy-3-nonyl) adenine, an adenosine deaminase inhibitor, was also examined for inhibitory potency with mammalian purine nucleoside phosphorylase, and was observed to be a competitive inhibitor of this enzyme, with an inhibition constant of 1.90 × 10 −4 m. The Michaelis constant for the substrate guanosine was near 6.0 × 10 −5 m. Physical probe of the nature of the functional groups which participate in enzymic catalysis implicated both histidine and cysteine as the essential catalytic species. Photooxidation studies suggested a pH-dependent sensitivity of an essential catalytic group, and its probable location at the active site.

Directional acoustic measurements by laser Doppler velocimeters

Laser Doppler velocimeters (LDV’s) are used as velocity microphones to measure sound pressure level in the range of 90–130 dB, spectral components, and two-point correlation functions for acoustic noise source identification. Close agreement between LDV and microphone data is observed. Directional sensitivity and the ability to measure remotely make LDV’s useful tools for acoustic measurement where placement of any physical probe is difficult or undesirable, as in the diagnosis of jet noise.

Circular dichroism as a probe of DNA structure inside reconstituted nucleo-histones

Reconstituted nucleohistones were obtained by mixing in given conditions acid extracted histones and eukaryotic DNA. The histone/DNA ratio (w/w) was in the range 0.35 - 0.95. With the four histones (H2A2B) we have been able to obtain subunits (nucleosomes or upsilon-bodies). The variation of cirsular dichroism signal with temperature at 280 nm was measured to follow structural changes of the DNA inside the complex. The true change of ellipticity (see article) of histone-bound DNA regions, is similar for reconstituted nucleohistone and H1-depleted chromatin, and is therefore a physical probe of the presence of nucleosomes.

ChemInform Abstract: FOUR‐POINT PROBE MEASUREMENTS ON N‐TYPE SILICON WITH MRCURY PROBES SEVERIN, P. J.

Chemischer InformationsdienstVolume 6, Issue 13 Physical Inorganic Chemistry ChemInform Abstract: FOUR-POINT PROBE MEASUREMENTS ON N-TYPE SILICON WITH MRCURY PROBES SEVERIN, P. J. H. BULLE, H. BULLESearch for more papers by this author H. BULLE, H. BULLESearch for more papers by this author First published: April 1, 1975 https://doi.org/10.1002/chin.197513019AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume6, Issue13April 1, 1975 RelatedInformation

ChemInform Abstract: PURINE CARBON‐8 SUBSTITUENT AS PROBE OF THE ELECTRONIC STRUCTURES OF ADENINE AND GUANINE, A COMPUTATIONAL STUDY

Chemischer InformationsdienstVolume 5, Issue 46 Physical Organic Chemistry ChemInform Abstract: PURINE CARBON-8 SUBSTITUENT AS PROBE OF THE ELECTRONIC STRUCTURES OF ADENINE AND GUANINE, A COMPUTATIONAL STUDY FRANK JORDAN, FRANK JORDANSearch for more papers by this author FRANK JORDAN, FRANK JORDANSearch for more papers by this author First published: November 19, 1974 https://doi.org/10.1002/chin.197446081Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume5, Issue46November 19, 1974 RelatedInformation