Small Size Scale Research Articles

Size Effects Determined from Tensile Tests of Perforated MEMS Scale Specimens

AbstractA systematic study of small-scale size effects has been conducted on elliptically perforated specimens with minimum radius of curvature of 1 micron. This study aimed at assessing the dependence of failure stress at the tip of a notch on varying: (a) stress concentration for constant radius of curvature, (b) radius of curvature of micro-notches relative to the material grain size and constant stress concentration. The experiments demonstrate a strong influence of notch radius on the failure strength of MEMS scale specimens, while the effect of the stress concentration factor is of rather secondary importance. The local failure strength at the tip of a notch increases when the radius of curvature becomes smaller, which is in accordance with the probabilistic nature of failure. When the notch radius becomes as small as 1 micron (only three times larger than the grain size) then a strong size effect is observed. This effect becomes moderate for larger radii of curvature, up to 8 microns (25 times the grain size), when the failure stress at the notch tip almost reaches the tensile strength recorded for 50 micron wide samples.

Magnetic Field Generation and Subsequent Field Dissipation with Plasma Heating in Relativistic Streaming Pair Plasmas

Relativistic plasma streaming in background plasmas becomes unstable against the Weibel-type electromagnetic instability, which is one of effective mechanisms of magnetic field generation in cosmic plasmas. It is shown by using 3-D fully relativistic particle-in-cell (PIC) simulation code that magnetic fields perpendicular to the stream in an electron-positron (pair) plasma are generated in the early stage of the instability with small-scale sizes of the electron skin-depth. In the subsequent nonlinear stage there occurs magnetic reconnection which causes to make large-scale structure of magnetic fields in pair plasmas. The magnetic field dissipation through the magnetic reconnection leads to heating of the background plasma. These sequential physical processes are important for understanding of magnetic field generation in the relativistic shock of gamma-ray burst (GRB) sources in astrophysical plasmas.

Micromechanics-based variational estimates for a higher-order nonlocal constitutive equation and optimal choice of effective moduli for elastic composites

A generalization of the Hashin–Shtrikman variational formulation to random composites, due to J.R. Willis, is employed to derive micromechanics-based variational estimates for a higher-order nonlocal constitutive equation relating the ensemble averages of stress and strain, for a class of random linear elastic composite materials. We analyze two-phase composites with any isotropic and statistically uniform distribution of phases (which themselves may have arbitrary shape and anisotropy), within a formulation accounting for one- and two-point probabilities, and derive an explicit nonlocal constitutive equation that includes terms up through the fourth gradient of average strain. The analysis is carried out first for an arbitrary comparison medium. Then, a new approach is outlined and applied which employs the nonlocal correction to determine the optimal choice of comparison medium, and hence the optimal effective modulus tensor (as well as the optimal tensor coefficients of the nonlocal terms) for the amount of statistical information employed. The new higher order analysis provides a highly accurate nonlocal constitutive equation, valid down to quite small volume size scales and to rather strong variations of average strain with position. Among several applications illustrated, it permits accurate analytical assessment of the remarkably small predictions derived by Drugan and Willis (1996. Journal of the Mechanics and Physics of Solids 44, 497–524) of the minimum representative volume element (RVE) size needed for accuracy of the standard constant-effective-modulus macroscopic constitutive equation for elastic matrix-inclusion composites that have spherical inclusions/voids. It also affords an analytical assessment of the improved (i.e., reduced) minimum RVE size scale, compared to a standard constant-effective-modulus constitutive equation, to which the leading-order nonlocal constitutive equation derived by Drugan and Willis applies. This improvement is shown to be dramatic in some example cases.

Electrostatic dust modes in self-gravitating dense dusty plasmas with high fugacity

Self-gravitational instabilities in dusty plasmas have been investigated over different regimes of dust fugacity. The Jeans instability associated with dust-acoustic waves is shown to exist in the low fugacity regime. On the other hand, in dense dusty plasmas characterized by high fugacity, the instability is found to occur at much smaller scale sizes, and is associated with dust-Coulomb waves. The general case of arbitrary fugacity corresponding to dust charge-density waves and the associated Jeans instability has also been discussed. A comparison between the critical Jeans lengths for the different cases has been carried out.

Comparisons of rank-based methods and normal theory methods for unbalanced one-way repeated measures data

In this article, rank-based methods are developed for analyzing unbalanced one-way repeated measures data. It is assumed that errors within each subject are exchangeable random variables.R-estimates of the treatment effects are obtained by minimizing a piecewise linear function. Rank-based methods are developed for testing the equality of the treatment effects. An unbalanced data set is analyzed for illustrative purposes. The relative efficiency of theR-estimates and maximum likelihood estimates is discussed. A small scale simulation study, comparing powers and sizes of the rank-based tests and normal theory tests (e.g., Wald and F), is presented.

<i>Letter to the editor</i>CUTLASS observations of a high-m ULF wave and its consequences for the DOPE HF Doppler sounder

Abstract. The CUTLASS (Co-operative UK Twin Located Auroral Sounding System) Finland HF radar, whilst operating in a high spatial and temporal resolution mode, has measured the ionospheric signature of a naturally occurring ULF wave in scatter artificially generated by the Tromsù Heater. The wave had a period of 100 s and exhibited curved phase fronts across the heated volume (about 180 km along a single radar beam). Spatial information provided by CUTLASS has enabled an m-number for the wave of about 38 to be determined. This high-m wave was not detected by the IMAGE (International Monitor for Auroral Geomagnetic Efects) network of ground magnetometers, as expected for a wave of a small spatial scale size. These observations over the first independent confirmation of the existence of the ground uncorrelated ULF wave signatures previously reported in measurements recorded from an HF Doppler sounder located in the vicinity of Tromsö. These results both demonstrate a new capability for geophysical exploration from the combined CUTLASS-EISCAT ionospheric Heater experiment, and provide a verification of the HF Doppler technique for the investigation of small scale ULF waves.Key words. Ionosphere (ionosphere – magnetosphere interactions) . Magnetospheric physics (magnetosphere – ionosphere interactions; MHD waves and instabilities)

Three‐dimensional simulations of the ionospheric plasma transport in the presence of the structured field‐aligned flows

Recent observations from the Preja and FAST satellites as well as earlier observations from OGO 5, Heos 2, and DE 2 indicate the presence of fine structures in the field‐aligned plasma flows. We have simulated the effects of such structures on ionospheric plasma transport processes, using our three‐dimensional large‐scale, multimoment, multifluid model. The model solves the continuity, momentum and double adiabatic energy equations with anisotropic ion temperatures in the field line coordinates from 1500 km to 10 RE. It includes important physics of the ionosphere‐magnetosphere coupling region, such as the mirror force and generalized ambipolar electric field in a dipole magnetic field geometry. Freja satellite observations of the structured field‐aligned currents were used as input parameters in the simulation. It has been shown that in the presence of the field‐aligned current filaments with sufficiently small transverse scale sizes, the transverse transport can play a dominant role in the overall plasma response processes in the ionosphere‐magnetosphere coupling region. For example, the local changes in parallel flow velocity due to transverse transport, l min after the structured field‐aligned current application, may be > 30%. The plasma response time due to transverse transport has been found to be shorter than that due to parallel transport. The difference is more pronounced at higher altitudes.

High-latitude HF Doppler observations of ULF waves: 2. Waves with small spatial scale sizes

Abstract. The DOPE (Doppler Pulsation Experiment) HF Doppler sounder located near Tromsø, Norway (geographic: 69.6°N 19.2°E; L = 6.3) is deployed to observe signatures, in the high-latitude ionosphere, of magnetospheric ULF waves. A type of wave has been identified which exhibits no simultaneous ground magnetic signature. They can be subdivided into two classes which occur in the dawn and dusk local time sectors respectively. They generally have frequencies greater than the resonance fundamentals of local field lines. It is suggested that these may be the signatures of high-m ULF waves where the ground magnetic signature has been strongly attenuated as a result of the scale size of the waves. The dawn population demonstrate similarities to a type of magnetospheric wave known as giant (Pg) pulsations which tend to be resonant at higher harmonics on magnetic field lines. In contrast, the waves occurring in the dusk sector are believed to be related to the storm-time Pc5s previously reported in VHF radar data. Dst measurements support these observations by indicating that the dawn and dusk classes of waves occur respectively during geomagnetically quiet and more active intervals.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions) · Magnetospheric physics (MHD waves and instabilities)

High-latitude HF Doppler observations of ULF waves: 2. Waves with small spatial scale sizes

The DOPE (Doppler Pulsation Experiment) HF Doppler sounder located near Tromsø, Norway (geographic: 69.6°N 19.2°E; L = 6.3) is deployed to observe signatures, in the high-latitude ionosphere, of magnetospheric ULF waves. A type of wave has been identified which exhibits no simultaneous ground magnetic signature. They can be subdivided into two classes which occur in the dawn and dusk local time sectors respectively. They generally have frequencies greater than the resonance fundamentals of local field lines. It is suggested that these may be the signatures of high-m ULF waves where the ground magnetic signature has been strongly attenuated as a result of the scale size of the waves. The dawn population demonstrate similarities to a type of magnetospheric wave known as giant (Pg) pulsations which tend to be resonant at higher harmonics on magnetic field lines. In contrast, the waves occurring in the dusk sector are believed to be related to the storm-time Pc5s previously reported in VHF radar data. Dst measurements support these observations by indicating that the dawn and dusk classes of waves occur respectively during geomagnetically quiet and more active intervals.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions) · Magnetospheric physics (MHD waves and instabilities)

The Space Density of Spiral Galaxies as function of their Luminosity, Surface Brightness and Scalesize

AbstractThe local space density of galaxies as a function of their basic structural parameters -like luminosity, surface brightness and scalesize-is still poorly known. Our poor knowledge is mainly the result of strong selection biases against low surface brightness and small scalesize galaxies in any optically selected sample. We show that in order to correct for selection biases one has to obtain accurate surface photometry and distance estimates for a large (≳ 1000) sample of galaxies. We derive bivariate space density distributions in the (scalesize, surface brightness)-plane and the (luminosity, scalesize)-plane for a sample of ~1000 local Sb-Sdm spiral galaxies. We present a parameterization of these bivariate distributions, based on a Schechter type luminosity function and a log-normal scalesize distribution at a given luminosity. We show how surface brightness limits and (1+z)4 cosmological redshift dimming can influence interpretation of luminosity function determinations and deep galaxy counts.

A [ITAL]z[/ITAL] = 5.34 Galaxy Pair in the Hubble Deep Field

?????The system as a whole is slightly brighter than L relative to the z ~ 3 Lyman break population, and the total star formation rate inferred from the UV continuum is ?22 h M? yr-1 (q0 = 0.5) assuming the absence of dust extinction. The two individual galaxies are quite small (size scales 1 h kpc). Thus these galaxies superficially resemble the building blocks of Pascarelle and coworkers; if they comprise a gravitationally bound system, the pair will likely merge in a timescale ~100 Myr.

Stress and strain in ferroelectrics

Ferroelectrics are being integrated into many structures, both large and small. Various innovations have once again brought the fundamentals of ferroelectricity into focus. Advances have been made in understanding stress and strain effects, especially on phenomena at small size scales. These phenomena include depoling and cracking in actuators, and properties of small free particles, fine grain ceramics and thin films.

New Species of Cnemaspis (Reptilia: Gekkonidae) from Southeastern Thailand

A new small species of Cnemaspis, C.chanthaburiensis, is described from Chantaburi & Chon Buri Provinces, Southeastern Thailand. It is the only Cnemaspis occuring in the region and may be distinguished from congeners by its small size (maximum 41 mm svl), smooth ventral and subcaudal scales, 7-9 preanal pores in males, and by hyperphalangy of digits II and V of the manus and digit II of the pes. The hyperphalangeal condition is unique Asian geckos.

A Holistic View of the Magnetic Field in the Eridanus/Orion Region

We present observations of 21 cm emission-line Zeeman splitting at 217 positions in the Orion/Eridanus loop region and incorporate them with stellar polarization data in a partially successful attempt to develop a holistic interpretation of the magnetic field structure on small and large size scales. We develop the "paraboloidal model" to describe the idealized perturbation to ambient magnetic field lines expected for a worm/chimney structure. We compare the magnetic field data to this model and find fair agreement for part of the region. On the small scale of one of the molecular clouds, previous interpretations invoke a helical field; in contrast, our interpretation invokes the Eridanus shock and its interaction with dense molecular clouds, in which the observed reversal in the line-of-sight field occurs naturally.

THE STOCHASTIC NATURE OF CARDIAC PROPAGATION DUE TO THE DISCRETE CELLULAR STRUCTURE OF THE MYOCARDIUM

The object of this paper is to describe cardiac conduction phenomena caused by the discrete nature of cardiac cellular structure. Recent results show that the myocardial architecture creates inhomogeneities of electrical load at the microscopic level that cause cardiac propagation to be stochastic in nature. That is, the excitatory events during propagation are constantly changing and disorderly in the sense of varying intracellular events and delays between cells. A unique feature of the stochastic nature of cardiac propagation is that electrical boundaries produced by cellular myocardial architecture create inhomogeneities of electrical load that affect conduction inside individual cells and influence conduction delays across gap junctions, as well as at muscle bundle junctions. This process produces discontinuous propagation as a primary reflection of the nonuniformities of electrical load due to the irregular arrangement of the cellular borders and the associated nonuniform distribution of their electrical interconnections. A fundamental consequence of the stochastic nature of normal propagation at a microscopic level is that it provides a major protective effect against arrhythmias by re-establishing the general trend of wave front movement after small variations in excitation events occur. When the diversity at a very small size scale decreases throughout the tissue, such as occurs when there are regularly repeating relatively isolated groups of cells, larger fluctuations of load can develop and be distributed over more cells than occurs normally. The myocardial architecture may then fail to re-establish a smoothed wave front and re-entry can develop. These relatively new discontinuous conduction phenomena provide important theoretical and experimental challenges to synthesize a complete theory linking continuous and discontinuous media as applied to cardiac conduction. The results show that it will be important to distinguish differences in wave front movement and conduction block caused by mechanisms of continuous media versus wave front movement and block imposed by directional or localized changes in cellular connectivity; i.e., the topology of the electrical connections between cells (gap junctions).

Lynds 1527: An Embedded Protobinary System in Taurus

Submillimeter continuum maps at 800 μm of the embedded source IRAS 04368+2557 in L1527 in Taurus show that there are two sources separated by 20'', or 2800 AU. The secondary source is between 2 and 3 times less luminous than the primary source if both sources have similar spectral energy distributions. Large-scale C18O J = 1 → 0 emission shows the sources to be embedded in a single dense core, and observations of C18O and C17O show the sources to be associated with a compact region of high-density gas. Three transitions of C18O show a velocity gradient between the two sources. On the smallest size scale, the C18O J = 3 → 2 emission has a velocity gradient of 3-7 km s-1 pc-1. The proximity of the sources in both space and velocity suggest that they are a very young protobinary system. The estimated age of the primary source, 5 × 103 yr, is much less than the estimated orbital period, 1.4 × 105 yr. The separation and young age of the system indicates that it formed through fragmentation of the dense core during collapse.

Mechanics of dilatant transformation in one side of bimaterial interface

The interface toughening owing to the phase transformation in one side of the bimaterial interface is modelled. As the first step for the modelling, an alternative analysis of a transformation strain spot interacting with the interface crack to that of Suo [Singularities interacting with interfaces and cracks. Int. J. Solids Structures 25, 1133–1141 (1989)] is presented through developing the weight function method presented by Paris et al. [The weight function method for determining stress intensity factors. Crack and Fracture, ASTM-STP 601, 471–489 (1976)] for the interface crack problem. Under a small scale transformation condition, the shape and size of the transformation zone, the energy release rate change G tip/ G and the phase angle shift Δψ = ψ tip − ψ of the near-tip intensity K tip relative to the applied remote K is computed. Besides, it is revealed that the interface crack flanks will be closed owing to the transformation near the crack tip within some parameter limits. A criterion determining the interface toughening is given, which shows that the interface toughening effect is not only contributed to by the energy release rate changes G tip/ G but also by the phase angle shift Δψ, and that it is a function of the phase angle ψ of the remote K. For the pure dilatant transformation toughening, the interface toughening effect changes greatly with the phase angle ψ of the remote K.

On the ductile to brittle transition in martensitic stainless steels — Mechanisms, models and structural implications

A new model of quasi-cleavage fracture toughness and the quasi-cleavage to microvoid coalescence transition is described. Quasi-cleavage occurs when stresses above a critical level encompass a critical area ahead of a crack tip. The underlying mechanism is a stable-to-unstable growth transition of a process zone crack. High toughness can be associated with the quasi-cleavage, particularly in cases involving shallow cracks and small size scales. A mixed quasi-cleavage-microvoid coalescence fracture mode transition occurs when the strains in the process zone exceed a critical level. Coupling these material properties with finite element calculations provides a physical basis for predicting the effects of size, geometry, loading rate and specified failure conditions relevant to actual structures using data from subsized specimens.

On dislocation storage and the mechanical response of fine scale microstructures

For lamellar aggregates, a small size scale is attained where flow in a ductile layer occurs by the motion of single dislocations rather than dislocation arrays. Analysis of such a case indicates that the flow stress should follow an Orowan-type relation accompanied by rapid effective work hardening. Consequences for flow instability and fracture are considered.

Peculiar human resource management practices?: A case study of a microstate hotel

This article explores the alleged pecularities of human resource management practices in very small developing states. A number of theoretical and ideo-typical features are culled from a literature review and are subsequently confronted with the empirical reality of human resource practices at Southern Bliss Hotel, a large, four-star tourist complex in Malta, the Mediterranean microstate. It is suggested that there are idiosyncracies to management issues in small size and small scale territories which call for recognition on their own terms. Some implications of these observations for hotel human resource management are explored.