Microscopic Units Research Articles

Shape anisotropy and magnetic domain structures in striped monolayers

We study the effect of dipolar interactions on a magnetic striped monolayer with a microscopic unit cell of square symmetry, and of size $(N_x\times N_y)$ spins. Even if the aspect ratio $r=N_x/N_y$ is very large, an in-plane shape anisotropy is always negligible, except if $N_y$ is fairly small $(N_y<40)$. In-plane domains are not possible, except for values of the dipolar coupling larger than the domain wall energy.

Spectral Characteristics and Colloidal Properties of Chlorophyll a‘ in Aqueous Methanol

The “phase behavior” of chlorophyll a‘ (Chl a‘, C132-epimer of Chl a) dissolved in aqueous methanol was examined in terms of the composition of the solvent. This study aimed at elucidating the property of Chl a‘, the exotic pigment found in a photosynthetic reaction center complex, as well as at clarifying the nature of the Chl aggregation in aqueous media. Visible absorption, circular dichroism (CD), fluorescence and resonance Raman spectroscopies, dynamic light-scattering measurements, and electron microscopy were utilized. Chl a‘ formed either of two types of colloids depending on the solvent composition. The one formed over a wide methanol volume percentage (ca. 73−30%) commonly possessed a single microscopic structural unit that yielded the double-peaked absorption (ca. 690 and 715 nm) accompanied by a symmetric dispersed-type CD spectrum. Increasing methanol concentration within this solvent composition range enhanced the size of the colloid and finally caused critical opalescence, which was reminiscent of the critical behavior of the aqueous solution of nonionic surfactants. These findings indicate that the microscopic structure of the Chl a‘ aggregate was independent of the size and shape of the colloid. This is in sharp contrast to the solvent composition dependence of the Chl a aggregation in the same medium: an increase in methanol concentration in going from 40% to 70% (vol/vol) shifted a broad red-most absorption band from ca. 700 to 750 nm, which was correlated to the enhancement of the aggregation number and the colloidal size. The difference between the aggregation behaviors of Chl a and a‘ suggests a narrower choice of possible molecular arrangements in the Chl a‘ aggregate as an inherent property of the pigment. The nature of the Chl aggregation in aqueous media is discussed in relation to the micellization of nonionic surfactant.

Quantitative implementation of Preisach‐Mayergoyz space to find static and dynamic elastic moduli in rock

In this paper we describe the analysis of quasi‐static stress‐strain data using a Preisach‐Mayergoyz (PM) [after Preisach, 1935; Mayergoyz, 1985] space picture for the elastic behavior of rock. In contrast to the traditional analytic approach to stress strain (an energy density as a function of the strain invariants), the PM space picture reproduces hysteresis and discrete memory seen in the data. In addition, the PM space picture establishes a relationship between experimental data and a number density ρ of microscopic mechanical units within the rock. The density ρ allows us to make quantitative predictions of dynamic elastic properties. Determining ρ from quasi‐static stress‐strain data requires us to solve a highly underdetermined inverse problem. We explore the following three methods of solving the inverse problem: simulated annealing, normal modes, and exponential decay. All three methods are tested on a Berea sandstone data set and found to give an excellent description of stress versus strain. Choosing one method, the normal mode method, we analyze quasi‐static stress‐strain curves on two additional sandstones, namely, another sample of Berea and a sample of Castlegate sandstone. From the density ρ for each sample we predict the dynamic modulus as a function of pressure and the nonlinear elastic constants. For each of these cases the agreement between the predictions based on ρ and experiment is quite good. We establish that PM space provides a quantitative description of the elastic response of a rock and that PM space may be found by a variety of inversion methods.

Internal Friction of (SiO2)1-x (GeO2)x Glasses

Internal friction of (Si0 2 ) 1-x (Ge0 2 ) x glasses (x = 0, 5, 10, 24 and 100 mole%) is measured at temperatures between 1.6 and 280 K. The data are fitted with the equations for thermally activated relaxation with distributing activation energies in symmetrical double-well potentials. From the determined relaxation strength spectra for each sample, the contributions from each type of microscopic structural units are calculated assuming that transverse motion of the bridging O atom in Si-O-Si, Si-O-Ge or Ge-O-Ge bridge (T model) is the microscopic unit responsible for relaxation. For instance, the magnitude of internal friction for Si0 2 -5% Ge0 2 or 24% GeO 2 is calculated from the data of pure Si0 2 , Si0 2 -10% Ge0 2 and pure Ge0 2 . The calculated results agree well with the measurements of Si0 2 -5% Ge0 2 and Si0 2 -24% Ge0 2 . Thus T model is shown to be quantitatively consistent with internal friction of SiO 2 -GeO 2 binary glasses.

Simulation of gas exchange and pulmonary blood flow using a water-displacement model lung.

The transport of oxygen by blood to the tissues begins at the lungs. Here fresh inspired oxygen diffuses into the blood while metabolically produced carbon dioxide diffuses out of the blood. To perform this simple function the lungs require a large surface area. This is achieved by the lungs having a complex sponge-like structure, consisting of millions of microscopic gas-exchanging units each with their own blood supply. In the healthy lung these myriads of units can be treated as one large unit. This simplification has allowed the development of numerous mathematical models describing lung ventilation, gas exchange and perfusion. The simpler mathematical models consist of just three compartments: a dead space, Vd (the ventilated but non gas-exchanging airways of the lungs), an alveolar volume, Va (the combined volume of the gas exchange units) and a gas-exchanging blood volume, Qp (pulmonary blood flow). Many of these mathematical models make further simplifications and assume that the ventilation of the lungs is continuous rather than tidal.KeywordsDead SpaceCarbon Dioxide ConcentrationPulmonary Blood FlowAlveolar SpaceAlveolar VolumeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

How the unit cell surface charge distribution affects the energetics of ion–solvent interactions in simulations

The evaluation of the electrostatic potential in condensed phase simulations normally includes an ‘‘extrinsic’’ contribution that manifests natural imbalances in the surface charge distribution of the microscopic unit cell. Most directly affected are ion–solvent interaction energies, and depending on whether the specific simulation conditions eliminate the extrinsic potential or not, these energies can vary by a considerable amount. This is illustrated by examining simulations of dilute aqueous solutions of Cl− and Fe2+ that use either a cutoff scheme or Ewald summation. It is found that the ion–water potential energy can vary with the type of boundary condition by as much as ≊60 kJ mol−1 for Cl− and ≊800 kJ mol−1 for Fe2+. The difference is exclusively due to the extrinsic potential effect and it is easy to calculate an appropriate correction term.

Phoneme labeling of frame by accumulating evidence obtained from spotting results of microscopic units

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Element absorption and hydration potential of polyacrylamide gels

Abstract Element absorption and hydration potential (HP) of two polyacrylamide gels (Aa and Bb) were studied after incubation in Hoagland's nutrient solution concentrations of either 2X, 1X, 0.5X, 0.25X, 0.125X, or 0X (deionized water). Element absorption was observed and analyzed by making transects from the gel granule surface to center on a Phillips CM12S scanning transmission electron microscope (STEM) equipped with an EDAX 9800 plus EDS unit for x‐ray micro analysis. Thick sections were cut on dry glass knives using an RMC MT6000 ultramicrotome. Surface analysis of bulk specimens was also made with an AMR 1000A scanning electron microscope plus PGT1000 EDS unit. Overall, gel HP decreased curvilinearly as solution concentration increased linearly; however, HP was generally higher for gel Bb than for Aa. Surface analysis of both gels compounds (1X concentration) revealed the presence Ca, Zn, and K. Additionally, Mn, S, and P in trace amounts, and Fe were found at the surface of gel Aa. Furthermore, Fe ...

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Journal Article Reply Get access Abbas Ali Mahdi, Abbas Ali Mahdi Department of Biochemistry, King George's Medical College, and Electron Microscope Unit, Central Drug Research Institute, Lucknow, India Reprints or correspondence: Dr. A. A. Mahdi, Department of Biochemistry, King George's Medical College, Lucknow 226003, India. Search for other works by this author on: Oxford Academic PubMed Google Scholar Virendra Kumar Bajpai Virendra Kumar Bajpai Department of Biochemistry, King George's Medical College, and Electron Microscope Unit, Central Drug Research Institute, Lucknow, India Search for other works by this author on: Oxford Academic PubMed Google Scholar The Journal of Infectious Diseases, Volume 166, Issue 4, October 1992, Page 938, https://doi.org/10.1093/infdis/166.4.938 Published: 01 October 1992

Microscopic origins of the interface friction of organic films: The potential of vibrational spectroscopy

This paper begins by reviewing the history of interface friction of organic films in terms of the measurement and interpretation of these phenomena using microscopic models. The interface friction is considered to arise from the shear or flow of the organic film and the prime characteristic is taken as the interface shear stress, denoted as τ. The influence of contact pressure, temperature and sliding velocity is described in general terms. The essence of the established models is based upon the belief that microscopic entities, such as side groups or chain segments, are engaged within the shear plane and thereby transfer frictional work into the film which is ultimately dissipated as heat by phonon wave damping. The value and success of these models is assessed. An alternative approach is suggested which seeks to use vibrational spectroscopy as a means of identifying the characteristics of the microscopic units active in the shear plane. The data are preliminary, but indicate that this method has potential for identifying the species responsible for accommodating the microscopic strain and also for characterizing the environment in which these species flow.

Residual monomer and pendant methacryloyl group in light-cured composite resins.

Microareas (100 x 100 microns 2) of thin visible light-cured composite sections irradiated for 10-60 s were analyzed with a Fourier transform infrared spectrometer equipped with a microscopic unit before and after extraction of residual monomers to determine the percent unreacted double bonds (UDB) and percent pendant double bonds (PDB). The percent eluted double bonds (EDB) was calculated using these percents. Analysis was conducted at various depths along the midline from the irradiated surface to the base. There were significant differences among the tested materials at each depth in UDB, PDB and EDB percents. The percent PDB of each material remained almost constant (25-40%) to a certain depth. This depth was equivalent to 70-80% of the depth of cure for each material. The range of depths at which percent PDB was constant indicated greater than 35-40% degree of conversion. At these locations, the composites may polymerize with a high rate of crosslinking.

Picorna‐like viral particles associated with mass mortalities in larval barramundi, Lates calcarifer Bloch

Journal of Fish DiseasesVolume 13, Issue 3 p. 245-249 Picorna-like viral particles associated with mass mortalities in larval barramundi, Lates calcarifer Bloch J. S. GLAZEBROOK, Corresponding Author J. S. GLAZEBROOK Graduate School of Tropical Veterinary Science, James Cook University, Townsville, AustraliaDr J. S. Glazebrook, Graduate School of Tropical Veterinary Science, James Cook University, Townsville, Queensland, AustraliaSearch for more papers by this authorM. P. HEASMAN, M. P. HEASMAN Sea Hatcheries Ltd, Mourilyan via Innisfail, Queensland, AustraliaSearch for more papers by this authorS. W. de BEER, S. W. de BEER Electron Microscope Unit, James Cook University, Townsville, Queensland, AustraliaSearch for more papers by this author J. S. GLAZEBROOK, Corresponding Author J. S. GLAZEBROOK Graduate School of Tropical Veterinary Science, James Cook University, Townsville, AustraliaDr J. S. Glazebrook, Graduate School of Tropical Veterinary Science, James Cook University, Townsville, Queensland, AustraliaSearch for more papers by this authorM. P. HEASMAN, M. P. HEASMAN Sea Hatcheries Ltd, Mourilyan via Innisfail, Queensland, AustraliaSearch for more papers by this authorS. W. de BEER, S. W. de BEER Electron Microscope Unit, James Cook University, Townsville, Queensland, AustraliaSearch for more papers by this author First published: May 1990 https://doi.org/10.1111/j.1365-2761.1990.tb00780.xCitations: 115AboutPDF 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 onFacebookTwitterLinked InRedditWechat Citing Literature Volume13, Issue3May 1990Pages 245-249 RelatedInformation

Unified study of the different physical properties of amorphous polymers

Uptil now it has not been possible to explain the different physical properties of amorphous polymers using a model based on a single conceptual scheme. In this paper, a phenomenological model is proposed which tries to explain the mechanical, optical and thermal properties (both thermal conductivity and expansivity) of amorphous polymers. The model has similarities with the composite model, proposed by the present authors, which has proved to be successful in interpreting the different physical properties of semicrystalline polymers. The present model considers the bulk form of the polymer as an aggregate of microscopic units possessing intrinsic physical properties. On drawing, the development of anisotropy in different physical properties is supposed to be due to the development of preferred orientation of these units. The development of the preferred orientation has been estimated directly from birefringence data. The agreement between the calculated and experimental values of the elastic modulus, thermal conductivity and thermal expansivity of PVC, PMMA and PS is found to be reasonable good.

Phonemic Recognition of Input Frames by Partial Matching Method Based on Continuous Dynamic Programming

AbstractThis paper proposes the partial matching method based on continuous DP, which is a new method to recognize the phoneme in continuous speech by pattern matching. The result of recognition experiment for the phoneme by the method is also shown. The standard pattern used in the continuous DP is a relatively macroscopic speech unit. The matching interval between the standard and the input patterns is labeled by a more microscopic speech unit, i.e., phoneme and pseudo‐phoneme. This is called the matching history, by the use of which, when the continuous DP values is less than a certain threshold, each input frame is identified using the phoneme and pseudo‐phoneme. For each input frame, the number of identifications for each phoneme or psuedo‐phoneme is calculated, and the result of recognition for the frame is determined as the phoneme or pseudo‐phoneme providing the maximum. The recognition experiment was made for the open data, composed of 19,440 frames uttered by 5 speakers, with 156 kinds of pseudo‐phonemes. The accumulated frame recognition rate was 57.6 percent for the first and 87.6 percent for the sixth. The accumulated pseudo‐phoneme recognition rate was 71.6 percent for the first and 90.1 percent for the sixth. The recognition system is of the frame‐wise form, and is suited to the realtime processing.

Statistical mechanics of mesoscales in neocortex and in command, control and communications (C3)

Most studies of neural and neural-like systems have focused on emergent collective properties of large numbers of microscopic units. When these details of microscopic interactions are coarse-grained, the utility of directly studying the aggregated mesoscopic scale of interactions becomes apparent, as has been demonstrated by a series of papers by the author: Detailed properties of neocortical phenomena, e.g., a derivation of the 7 ± 2 rule of short-term memory, its stability and duration, and spatial-temporal properties of electroencephalographic (EEG) and magnetoencephalographic (MEG) phenomena can be explicitly calculated and shown to agree favorably with empirical evidence. This mesoscopic scale is important, not only to achieve pattern recognition or to test the analysis of the microscopic scale, but indeed it is to be respected as a potential source of command and control over the microscopic scale, in both the brain, e.g., as a pre-attentive filter and processor of patterned information, and in other large-scale systems, e.g., in Command, Control and Communications (C3) systems.

Structural phase transition in SiO x

For the two structural phases of the geometrically and chemically disordered solid SiO x , i.e. the random-bonding and the random-mixture phase, the temperature-composition phase diagram is calculated in dependence on an ordering energy E o . It is shown that the random-bonding phase is the high-temperature structure of SiO x , which is metastable or even unstable at low temperatures, revealing there a spinodal decomposition into two coexisting components with different chemical compositions and random-mixture structure. The corresponding immiscibility dome has its highest point at the temperature T = 0.5 E o /k for x = 1 . The phase transition is of first order. The ordering energy E o depends on the interaction between the microscopic structural basic units, i.e. the Si-Si and Si-O-Si bonds, and is calculated in terms of the bond-orbital approximation. The value of E o does probably not exceed 0.15 eV. The results are in agreement with experimental experience. The predictions derived could induce systematic experimental investigations of the phase transition in SiO x and, especially, of its spinodal decomposition.

A new design of the scanning tunneling microscope unit

Abstract An STM unit has been designed and built, incorporating some new characteristics. The unit uses three piezotubes for scanning and a piezoelectric bimorph for the fine approach of the sample. The use of these materials avoids the need of high voltages, but maintains the capability of large scan lengths.

A new design of the scanning tunneling microscope unit

An STM unit has been designed and built, incorporating some new characteristics. The unit uses three piezotubes for scanning and a piezoelectric bimorph for the fine approach of the sample. The use of these materials avoids the need of high voltages, but maintains the capability of large scan lengths.

A high performance isolated rat brain preparation part I: Operative technique and recipient extracorporeal perfusion

The microsurgical preparation and high level performance with extracorporeal recipient perfusion of a stable, totally isolated rat brain model is presented. Emphasis has been placed on the use of the operating microscope, bipolar cautery and mechanical fixation units to affect a complete ablation of all non-osseous cephalic and vertebral tissues with minimal physiological disturbance of the animal as a whole. The simplified technique of recipient support circulation of the isolated brain organ achieves at least 5 h of tissue viability and function as measured by electrocortical activity, A- Vo 2 differences and morphological appearance. To date, no other isolated rodent brain model has been described which is truly anatomically separated from all cephalic tissues. Additionally, other surgical attempts at isolation have required the use of abnormal physiological states, including deep hypothermia and circulatory arrest.

A study of the dynamics of foam growth: Analysis of the growth of closely spaced spherical bubbles

AbstractA mathematical analysis of bubble growth in an expanding foam is presented. The analysis is based on a cell model whereby the foam is divided into spherical microscopic unit cells of equal and constant mass, each consisting of a liquid envelope (or shell) and a concentric spherical gas bubble. Expansion occurs by diffusion of a dissolved gas from the supersaturated envelope into the bubble. This cell model is capable of describing important qualitative features of a real system of numerous bubbles growing in close proximity to one another, and is intended as the building block of a global analysis of macroscopic foam expansion. The coupled algebraic and differential equations governing the growth of a cell are derived and solved numerically. Five dimensionless parameters are identified for the case of constant temperature and pressure outside the cell, and their effects are demonstrated through computer simulations of the system. Of these parameters, surface tension and initial radius prove to be of relatively little importance in the practical cases considered. The other parameters are the thermodynamic driving force, the cell mass (inversely proportional to the number density of bubbles), and the ratio of characteristic times for mass and momentum transport.