Pronounced Hump Research Articles

Polarization ratio and effective mass in InP nanowires: Effect of crystallographic axis

Indium phosphide nanowires grown along different crystallographic axes---namely, the [001], [101], and [111] directions of zinc-blende structure---are investigated using a first-principles derived semi-empirical pseudopotential theory, aimed at understanding the effects of wire orientation on band structure, polarization ratio, and effective masses of semiconductor nanowires. Band energies over entire Brillouin zone are determined, and are found to exhibit different characteristics for three types of wires in terms of band dispersion and the location of orbital energy. A pronounced dispersion hump is revealed to exist in the lowest conduction band for the [001] and [111] wires, but not for the [101] wires. On the other hand, the [001] and [111] wires are shown to have very different orbital energy for the top valence state at the zone boundary $X$ point---being $\ensuremath{-}6.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ in the former and $\ensuremath{-}6.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ in the latter. These differences provide specific and useful suggestion to encourage experimental determination of the band structure in InP nanowires. As another key result, we study the polarization ratio in wires of different orientations. Our calculations show that, given the same lateral size, the [111] wires yield the highest polarization ratio as compared to wires along the other two directions, while simultaneously possessing larger band-edge photoluminescence transition intensity. The [111] wires are thus suggested to be better suitable for optical device applications. Interestingly, we also found that polarization ratio displays a different size dependence than transition intensity does. More specifically, the polarization ratio is predicted to increase with the decreasing size, which is opposite to the behavior as exhibited by the optical transition intensity. The polarization ratios in the [101] and [111] wires of $11.7\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ diameter are shown to approach the limit of 100%. In addition to polarization ratio, we further determine the electron and hole masses for wires of different crystallographic axes. For the [101] and [111] wires, the hole masses are revealed to be $\ensuremath{\sim}0.25$, which are markedly smaller than the values $(\ensuremath{\geqslant}1.0)$ along the same direction in bulk. This result demonstrates an interesting possibility of obtaining in nanowires a high hole mobility that is not available in bulk. An explanation for the anomaly in the hole mass is suggested and is associated with the existence of an electronic band transition.

Electron tunneling experiments on La-substituted Kondo-semiconductor CeRhAs

Polycrystalline Ce 1− x La x RhAs is investigated by means of break-junction tunneling. On Ce substituted by La ( x = 0.01 ), a pronounced hump structure is developed at the bias ±0.25 V with a shallow dip on it. The hump emergence is consistent with a drastic reduction in the resistivity. These facts give direct evidence for the appearance of mid-gap states near the Fermi energy by a small La substitution for Ce in CeRhAs.

Anomalous magnetoresistance in [ Sr2Bi2-xPbxO4] RS[ CoO2] y (x = 0, 0.3, and 0.4; y ≈ 1.85) single crystals

Magnetoresistance (MR) of the [ Sr2Bi2-xPbxO4] RS[ CoO2] y (x = 0, 0.3, and 0.4; y ≈ 1.85; RS is referred to rocksalt block) single crystals is investigated systematically. A nonmonotonic variation of the isothermal in-plane and out-of-plane MR with the field is observed. The out-of-plane MR is positive at high temperatures and increases with decreasing T, and exhibits a pronounced hump, then changes the sign from positive to negative at a certain temperature. These results strongly suggest that the observed MR consists of two contributions: one negative and one positive component. The isothermal MR in high magnetic fields follows a H2 law. The negative contribution comes from spin scattering of carriers by localized-magnetic-moments based on the Khosla-Fischer model.

Influence of strong heterocoordination on surface properties of Li–Pb melts

The influence of the strong heterocoordination tendency of the Li–Pb liquid alloy on its surface properties has been studied using a statistical thermodynamic model based on compound formation and that based on the layered structure near the interface. In addition to the already proposed saltlike structure Li4Pb compound formed in the liquid alloy, the study shows that the compound Li3Pb also has a profound influence on the thermodynamic properties of the liquid alloy. The surface study suggests that the formed compounds in the liquid alloy segregate to the surface about 0.8 atomic fraction of Li. The calculated surface tension of the liquid alloy exhibits a pronounced hump above equiatomic composition.

Magnetic and electrical properties of a novel compound U 2Pd 2Pb

A new uranium plumbide U 2Pd 2Pb has been synthesized and studied by means of magnetization and electrical resistivity measurements. The compound crystallizes with the tetragonal structure of the Mo 2FeB 2-type. It orders antiferromagnetically at T N = 65 K and undergoes a change to different antiferromagnetic structure at T 1 = 20 K. In the paramagnetic region, the magnetic susceptibility follows a modified Curie–Weiss law with the effective magnetic moment μ eff = 2.46 μ B per U atom. Above T N the electrical resistivity exhibits a Kondo-like behavior, whereas in the ordered state a pronounced hump in the temperature dependence of the resistivity is observed that likely indicates the antiferromagnetic unit cell being larger than the chemical one.

Magnetic properties of a Tb 5Sn 3 single crystal

Single crystals of Tb 5Sn 3 have been successfully grown by the Czochralski method. Paramagnetic susceptibility of Tb 5Sn 3 obeys Curie–Wiss law and effective paramagnetic moment obtained from reciprocal susceptibility is 10.3 μ B along the c-axis and 10.0 μ B in the c-plane; paramagnetic Curie temperatures along the c-axis and in the c-plane are −0.78 and 22.2 K, respectively. Tb 5Sn 3 takes antiferromagnetic phase below T N = 62 K as reported by Semitelou and Yakinthos; a metamagnetic transition or a spin flop was observed at 4.2 K under up to 50 kOe external magnetic field. Another magnetic phase can exist below T t = 3.8 K. Electrical resistivity along the c-axis shows a pronounced hump just below T N due to a superzone gap formation along the new Brillouin zone boundaries.

A new and presumably extinct species of Ptychochromoides (Teleostei: Perciformes: Cichlidae) from central Madagascar

Ptychochromoides itasy, new species, is described from material collected from Lake Itasy and environs in the central highlands of Madagascar. The new species is distinguished from congeners by the presence of a pronounced occipital hump, regardless of size, sexual maturity, or sex, and also by a shorter predorsal length, more elongate terminal dorsal-fin spine, and shorter snout. Although reportedly once abundant in Lake Itasy, specimens referable to the new species have not been collected from the lake or surrounding region in several decades and the species is presumed to be extinct.

Adsorption of Oppositely Charged Polyelectrolyte/Surfactant Mixtures. Neutron Reflection from Alkyl Trimethylammonium Bromides and Sodium Poly(styrenesulfonate) at the Air/Water Interface: The Effect of Surfactant Chain Length

The interactions between a series of cationic surfactants (alkyltrimethylammonium bromides) (CnTAB) and the anionic polymer sodium poly(styrenesulfonate) (NaPSS) have been studied using surface tension and neutron reflectivity. The effect of surfactant chain length on surfactant/polymer adsorption has been studied using chain lengths from 10 to 16 carbon atoms (i.e. C10TAB to C16TAB). The surface tension plots (γ against ln c) have two types of shape. The C10TAB and C12TAB with NaPSS systems have plots with plateaus, while the longer chain C 14TAB and C16TAB systems have a pronounced hump in the surface tension at surfactant concentrations just below the critical micelle concentration (cmc) of the free surfactant. Neutron reflection shows that there is a surfactant monolayer (thickness 20−22 A) adsorbed at dilute surfactant concentrations for the C10TAB, C12TAB, and C14TAB systems, but this changes to a thick layer (60−100 A) at concentrations closer to the cmc. The corresponding areas per adsorbed surfac...

Evidence and characteristics of hydrolytic disproportionation of organic matter during metasomatic processes

Petroleum-geochemical analyses of carbonaceous regionally metamorphosed rocks, carbonaceous rocks from ore deposits, and alkalic plutonic rocks from diverse settings, demonstrated the presence of very low to moderately low concentrations of solvent-extractable organic matter, this observation in spite of the fact that some of these rocks were exposed to extremely high metamorphic temperatures. Biomarker and δ13C analyses established that the extractable organic matter originated as sedimentary-derived hydrocarbons. However, the chemistry of the extractable bitumen has been fundamentally transformed from that found in sediment bitumen and oils.Asphaltenes and resins, as defined in the normal petroleum-geochemical sense, are completely missing. The principal aromatic hydrocarbons present in oils and sediment bitumens (especially the methylated naphthalenes) are either in highly reduced concentrations or are missing altogether. Instead, aromatic hydrocarbons typical of sediment bitumens and oils are very minor, and a number of unidentified compounds and oxygen-bearing compounds are dominant. Relatively high concentrations of alkylated benzenes are typical. The polar “resin” fraction, eluted during column chromatography, is the principal compound group, by weight, being composed of six to eight dominant peaks present in all samples, despite the great geologic diversity of the samples. These, and other, observations suggest that a strong drive towards equilibrium exists in the “bitumen.” Gas chromatograms of the saturated hydrocarbons commonly have a pronounced hump in both the n-paraffins and naphthenes, centered near the C19 to C26 carbon numbers, and a ubiquitous minimum in the n-paraffin distribution near n-C12 to n-C14. Multiple considerations dictate that the bitumen in the samples is indigenous and did not originate from either surficial field contamination or from laboratory procedures.Our observations are consistent with the hydrolytic disproportionation of organic matter (HDOM), in which water and organic matter, including hydrocarbons, easily exchange hydrogen or oxygen with one another under certain conditions (Helgeson et al., 1993). The process appears to take place via well-known organic-chemical redox reaction pathways and is most evident in open-fluid systems. The conclusion that HDOM took place in the analyzed samples, thus producing the chemistry of the extractable bitumen, is supported by numerous previously published organic-geochemical studies of metamorphic, volcanic, plutonic, and ore-deposit-related rocks by other investigators.HDOM is suggested as an unrecognized geologic agent of fundamental importance. The process appears to control major chemical reactions in diverse geologic environments including, but not limited to, petroleum geology and geochemistry, regional metamorphism, and base- and precious-metal ore deposition.

High energy secondary peak structure in tunneling spectra (hump) as possible magnetic pseudogap

It is demonstrated that tunneling spectra in various high T c cuprates display generic features. The principal conductance peaks in superconductor-insulator-normal metal (SIN) junctions indicate the superconducting gap in the density of states (DOS). Higher energy features include a dip and hump structure with a strength that is asymmetric in bias voltage. The dip and hump features follow the doping trends of the superconducting gap, Δ, with a rough scaling as ∼2Δ and ∼3Δ respectively. Tunneling spectra in underdoped Bi 2Sr 2CaCu 2O 8+δ display a more pronounced hump feature suggestive of a second gap in the DOS. It is observed that the hump feature in the tunneling density of states is consistent with other experimental observations of the so-called high energy pseudogap which may have magnetic origins.

Cohort Analysis of Saving Behavior by U.S. Households

In this paper I analyze the pattern of saving behavior by U.S. households, using the Consumer Expenditure (CEX) Survey. The analysis' main goal is to explain the decline in aggregate personal saving in the United States in the 1980s. I estimate a typical' saving-age profile and identify systematic movements of the profile across different cohorts of U.S. households. In addition, I consider different definitions of saving and control for a number of factors that figure in popular explanations fo the decline in saving. The main results can be summarized as follows: 1) the typical' saving-age profile presents a pronounced hump' and peaks around age 60; 2) this typical' age profile was, at least during the 1980s, shifted down for those cohorts born between 1925 and 1939. This is consistent with the low level of aggregate saving because these cohort were, in the 1980s, in that part of their life cycle when saving is highest; 3) this results holds for various definition of saving with one notable exception; the decline is less pronounced when expenditure on durables is considered as saving; and 4) some other popular explanations of the decline in saving are rejected by the data, including those appealing to the presence of capital gains on real or financial assets.

Anomalous magnetoresistance behavior of R2Ni3Si5 (R = Pr, Dy, Ho).

Magnetoresistance (MR) measurements on the antiferromagnetically ordered polycrystalline ${R}_{2}{\mathrm{Ni}}_{3}{\mathrm{Si}}_{5}$ ($R=\mathrm{P}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{D}\mathrm{y},\phantom{\rule{0ex}{0ex}}\mathrm{H}\mathrm{o}$; ${T}_{N}=8.5 \mathrm{K}, 9.5 \mathrm{K}, 6.0 \mathrm{K}$, respectively) materials are reported here. Field dependence of MR, measured both below and above their respective ordering temperatures and up to a field of 45 kOe, is found to be anomalous. In all the three cases, in the magnetically ordered state, MR is not monotonic but exhibits a maximum and a minimum. A considerable contribution to MR, with nearly linear field dependence and persisting even above the magnetic ordering temperature, is observed, which is unusual. Temperature dependence of MR (in a constant high field) above the magnetic ordering temperature, measured up to 100 K, exhibits a pronounced hump. The behavior of magnetoresistance at low temperatures is interpreted in terms of metamagnetism along with a short range ferromagnetic interaction.

Retinoid-Induced Nasal Malformations

Treatment of pregnant Sprague-Dawley rats with etretinate or retinoic acid on pregnancy days 8.5-9.0 resulted in craniofacial defects in all embryos. A morphological investigation of the malformations occurring in the nasal region is described. The external nose was deformed with a depressed nasal bridge and pronounced hump. Fusion between nasal processes was defective, resulting in fistulas and clefts. The nasal septal cartilage was reduced in size, the paranasal cartilage was missing, the parietothecal cartilage was deformed and the paraseptal cartilage was dislocated. Aberrant vessels were seen on the external nose in combination with underdevelopment of the vibrissae. The distance between the outer nasal pores was reduced after administration of retinoids.

Field-ion energy spectroscopy of gold overlayers on silicon

Unoccupied localized states of the Au/Si(111) contact have been observed by means of field-ion energy spectroscopy. Gold overlayers of 3–5 ML thickness and greater were prepared and an intermixed SiAu structure was formed at this interface. The spectroscopic result in the form of integral field-ion energy distributions confirmed the existence of empty electronic states beginning at the Fermi level. A pronounced hump in the distribution was evaluated and resulted in a high density of states at 0.95±0.2 eV above the top of the valence band. For technical reasons, the spectroscopy was carried out with p-type Si. Using gold-covered n-type Si, Schottky barrier heights of the Au/n-Si(111) contact can be determined.

FIELD-ION ENERGY SPECTROSCOPY OF GOLD OVERLAYERS ON SILICON

By means of field-ion energy spectroscopy unoccupied localized states of the Au/Si(111) contact have been observed. Gold overlayers of 3-5 monolayers and greater were prepared. Under these conditions, an interface of intermixed Si-Au structure was formed. The spectroscopic result in the form of an integral field-ion energy distribution proved the existence of empty electronic states beginning at the Fermi level. A pronounced hump in the distribution was evaluated and resulted in a high density of states at (0.95 ± 0.2)eV above the top of the valence band edge. For methodical reasons the spectroscopy is carried out with p-type Si. Using gold-covered n-type Si, Schottky barrier heights of the Au/n-Si(111) contact can be determined.

A Poisson–Boltzmann treatment of the capacitance of a layer of symmetrical spherical dipoles

The capacitance of a layer of spherical orientable dipoles has been determined. The properties attributed to each dipole are those of two point charges on a diameter of the sphere and equidistant from its centre. A one-dimensional potential distribution is assumed to exist normal to the layer and to be coupled to the charge distribution via Poisson's law. The orientation of the dipoles is random in the absence of polarization, but is taken as governed by Boltzmannian statistics when an applied field is present. The treatment predicts that the capacitance will display a pronounced hump at the point of zero charge. Though this study was motivated by a wish to interpret the inner-layer capacitance at a mercury/aqueous electrolyte solution interface, the treatment is shown to be inapplicable quantitatively to such a system.

Subcritical detection using computer-generated tones and noise

Tones and variable-bandwidth noise generated by computer are used to determine the course of subcritical thresholds versus noise bandwidths. Computer usage permits control of parameters otherwise uncontrollable, namely, the mean intensity of individual noise presentations and the starting phase of tones re noise. Computer filtering also permits tests to range over noise bandwidths of 1.25 to 640 Hz, essentially encompassing the continuum from tone-on-tone discrimination to tone detection in wide-band noise. Though the two frozen noises used throughout the tests had identical presentation mean intensities, two significantly different threshold-noise bandwidth curves emerged, one fitted subcritically, by a straight line rising 3 dB per octave, the other by a curve exhibiting a pronounced hump between the 10- to 40-Hz noise bandwidth region. These results, which contradict the contention that energy ratios alone determine subcritical thresholds, were linked to two features of the noise, the differences in the concentrations of energy in the signal onset region and the presence of signal-like excursions of the envelope.

Adsorption of Thiourea and Derivatives at the In‐Hg Electrolyte Interface

The double layer capacitance and interfacial tension of polarized Hg, In, and In‐Hg (10 to 60 mole percent [m/o] In) electrodes were measured in 0.1M perchloric acid in a mixture of potassium chloride and hydrochloric acid (pH 1.6) and in the electrolytes containing thiourea and derivatives using the galvanostatic charging technique. Addition of thiourea increases the capacitance of the mercury electrode over the whole range of potentials. With the In‐Hg electrodes, thiourea addition depresses the capacitance over a range of anodic potentials and increases the values over a range of cathodic potentials. A pronounced hump in the capacitance curve is observed; the nature of the hump and the depression of the capacitance are markedly influenced by the presence of Cl−. These results are interpreted in terms of a reorientation of the adsorbed species in the interface. Effects of substituent groups on the above behavior were investigated using S‐methyl isothiourea and tetramethyl thiourea.

Positron Annihilation in Yttrium and Zirconium

The angular dependence of the positron annihilation radiation along the [0001] direction has been studied in yttrium and zirconium by the augmented-plane-wave method. The calculation was performed using a mesh of 250 points distributed uniformly throughout the $\frac{1}{24}$ zone. A set of 32 reciprocal lattice vectors was used to determine the eigenvalues and eigenfunctions. Exchange was treated in the Slater's ${\ensuremath{\rho}}^{\frac{1}{3}}$ approximation. The calculated curve for yttrium shows a fairly good agreement with the experimental results of Williams and Mackintosh. The theory predicts a more pronounced hump in the curve near the zone boundary than is observed experimentally. The experimental data for zirconium are not available, but the calculation shows that the hump almost disappears as the $d$ shell starts filling in.

Effective pullout of a cartilaginous graft in rhinoplasty.

THERE are times in the course of a rhinoplastic operation when a difficult decision must be made as to whether or not a cartilaginous graft should be used. I refer specifically to those cases in which minor depressions of the dorsal bridge or any part of the lateral walls are noticeable. It is possible that if these depressions are left alone, they may in time become filled with fibrous tissue and become unnoticeable. However, there is a greater risk that they will be very evident, thereby creating some obvious defects, such as a saddle nose if the dorsal bridge is very low, or a crooked nose if only one lateral wall is depressed. Yet even though the graft is carefully fitted to the defect in every dimension, it is possible that after several days have passed an unpleasant and pronounced hump may appear which is most disturbing to both