Abstract
Two-dimensional materials constitute a promising platform for developing nanoscale devices and systems. Their physical properties can be very different from those of the corresponding ...three-dimensional materials because of extreme quantum confinement and dimensional reduction. Here we report a study of TiTe
2
from the single-layer to the bulk limit. Using angle-resolved photoemission spectroscopy and scanning tunneling microscopy and spectroscopy, we observed the emergence of a (2 × 2) charge density wave order in single-layer TiTe
2
with a transition temperature of 92 ± 3 K. Also observed was a pseudogap of about 28 meV at the Fermi level at 4.2 K. Surprisingly, no charge density wave transitions were observed in two-layer and multi-layer TiTe
2
, despite the quasi-two-dimensional nature of the material in the bulk. The unique charge density wave phenomenon in the single layer raises intriguing questions that challenge the prevailing thinking about the mechanisms of charge density wave formation.
Modern underwater warfare necessitates the development of high-speed supercavitating torpedoes. Achieving supercavitation involves integrating a cavitator at the torpedo's front, making cavitator ...design a critical research area. The present study simulated supercavity formation by cavitators of various shapes attached to a heavyweight torpedo. The study involves simulations of thirteen cavitator designs with various geometrical configurations at different cavitation numbers. The simulations employ the VOF multiphase model along with the Schnerr and Sauer cavitation model to analyze supercavitation hydrodynamics. The study examines the supercavity geometry and drag characteristics for individual cavitator designs. The results reveal a significant reduction in skin friction drag by a majority of cavitators. Notably, a disc cavitator at a cavitation number of 0.09 demonstrates a remarkable 92% reduction in the coefficient of skin friction drag. However, the overall drag reduces when incorporating a cavitator, but it introduces additional pressure drag. The study found that the cavitators generating larger supercavities also yield higher pressure drag. Therefore, the supercavity should just envelop the entire torpedo, as excessively small supercavities amplify skin friction drag, while overly large ones elevate pressure drag. Ultimately, the study concludes that selecting the ideal cavitator entails a comprehensive evaluation of factors such as supercavity and torpedo geometry, reductions in skin friction drag and increments in pressure drag.
The current study reports the phenomenon of drop impacts on a hydrophobic surface in the substrate deposition regime (non-splashing), focusing on the characterization of each stage upon impact and ...different non-dimensional parameters involved such as spreading factor, recoil height and the durations of several phases. The results indicate that the drop dynamics is determined by an interplay of drop inertia, viscosity and surface tension. Apart from Reynolds number (Re) and Weber number (We) which are conventionally used to characterize drop impacts, a new non-dimensional impact parameter, ξ (= 〖We〗^(1/4) 〖Re〗^(1/5)) is introduced, and it is found out that the spreading factor and the different non-dimensional phase durations involved in the drop impact dynamics on a hydrophobic surface, scale fairly well with this newly defined impact parameter. Further, systematic studies into the non-dimensional durations of each phase upon impact, spreading factor and recoil factor (i.e. non-dimensional recoil height) with respect to different non-dimensional parameters are reported.
A high velocity ratio synthetic jet on an arched surface is of great interest for its potential applications in navy, including torpedo. However, in spite of detailed research on synthetic jets over ...a flat surface in cross-flow, very few observations have been made on synthetic jets over a surface which is shaped like a torpedo. This study experimentally explores a synthetic jet mounted on a torpedo shaped model in quiescent and cross-flow conditions. Initially, the synthetic jet is characterized for two different diaphragm displacements and at four distinct actuation frequencies in the range of 1 Hz – 6 Hz in a quiescent flow environment. Subsequently, in cross flow, similar study is conducted for three cross-flow velocities ranging from 7.2 – 32 cm/s, at a fixed amplitude of diaphragm oscillations. The measurements are carried out using Laser Induced Fluorescence (LIF) and Laser Doppler Velocimetry (LDV) and the qualitative LIF visualizations are corroborated by the quantitative LDV data. These results indicate that the synthetic jet vortex rings can be grouped as stretched vortex rings and distorted tilted vortex rings. The flow structures primarily depend on the velocity ratio, which is function of cross-flow velocity and frequency of actuation. The flow physics in case of a curved torpedo surface is slightly different as compared to the synthetic jet on a flat surface.
Gas transfer in a bubbly wake flow Karn, A; Gulliver, J S; Monson, G M ...
IOP conference series. Earth and environmental science,
05/2016, Letnik:
35, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The present work reports simultaneous bubble size and gas transfer measurements in a bubbly wake flow of a hydrofoil, designed to be similar to a hydroturbine blade. Bubble size was measured by a ...shadow imaging technique and found to have a Sauter mean diameter of 0.9 mm for a reference case. A lower gas flow rate, greater liquid velocities, and a larger angle of attack all resulted in an increased number of small size bubbles and a reduced weighted mean bubble size. Bubble-water gas transfer is measured by the disturbed equilibrium technique. The gas transfer model of Azbel (1981) is utilized to characterize the liquid film coefficient for gas transfer, with one scaling coefficient to reflect the fact that characteristic turbulent velocity is replaced by cross-sectional mean velocity. The coefficient was found to stay constant at a particular hydrofoil configuration while it varied within a narrow range of 0.52-0.60 for different gas water flow conditions.
Active treatment of BCEE (bis-2-chloroethyl ether) is being currently performed in the on-site Cohansey Aquifer at the Lipari Superfund Site. Remediation of BCEE in the underlying Kirkwood aquifer is ...being considered, necessitating investigations of BCEE geochemistry in aquifer material from the site. It is currently unknown to what extent BCEE is present in the dissolved, sorbed, or free-product phase in the Kirkwood Sand aquifer material. A series of partition coefficient sorption, column leach, and column loading tests were conducted to determine BCEE sorption to, and mobility in, the Kirkwood Sand aquifer material. The leach studies indicated that up to 50% of BCEE spiked (as free-phase product) onto two aquifer material column designs could be leached in approximately 18
h, due to the high aqueous solubility of BCEE. Dissolved BCEE concentrations then began to plateau as sorption reactions hindered further leaching, resulting in up to 80% removal after 48
h. Column loading and batch sorption experiments suggest that BCEE mobility is limited by sorption rather than solubility factors. Tracer tests in both column loading and batch sorption tests indicate sorption hinders leaching of BCEE from the Kirkwood Sand material.
Objective: To determine the effect of a continuous insulin infusion on protein and glucose metabolism in extremely low birth weight (ELBW) infants.
Study design: We measured the rate of appearance ...(Ra) of the essential amino acids leucine and phenylalanine (reflecting proteolysis), utilization of phenylalanine for protein synthesis, and glucose Ra using stable isotope tracers during a basal infusion of glucose (6 mg/kg/min) and in response to a continuous infusion of insulin (0.05 U/kg/hr) by means of the euglycemic hyperinsulinemic clamp technique. Four clinically stable, euglycemic ELBW infants (26 ± 0 weeks' gestation, 894 ± 44 gm birth weight, 2.8 ± 0.8 days of age) were studied.
Results: In response to a greater than tenfold increase in insulin concentration (from 7 ± 2 to 79 ± 13 μU/ml), there was a 20% decrease in leucine Ra (Basal: 272 ± 27 μmol/kg/hr; Insulin: 226 ± 29 μmol/kg/hr;
p < 0.01) and in phenylalanine Ra (Basal: 91 ± 5 μmol/kg/hr; Insulin: 72 ± 2 μmol/kg/hr;
p < 0.05). Use of phenylalanine for protein synthesis also decreased by a similar magnitude (Basal: 77 ± 4 μmol/kg/hr; Insulin: 62 ± 1 μmol/kg/hr;
p < 0.05). Glucose utilization doubled (from 8 ± 0.9 to 15.7 ± 1.1 mg/kg/min;
p = 0.0003) and plasma lactate concentrations tripled (from 2.1 ± 0.5 to 5.7 ± 1.0 mmol/L;
p < 0.05) during the insulin infusion.
Conclusions: During an infusion of glucose alone, pharmacologic concentrations of insulin in ELBW infants produced no net protein anabolic effect. Furthermore, euglycemic hyperinsulinemia was accompanied by development of significant metabolic acidosis. (J Pediatr 1998;132:948-53)
Infants with cyanotic congenital heart disease (CCHD) often have reduced weight gain compared with infants in control groups. Our purpose was to conduct a longitudinal study of energy intake, resting ...energy expenditure (REE), and total energy expenditure (TEE) of a group of infants with CCHD. We hypothesized that increased REE and TEE and decreased energy intake in these infants would lead to reduced growth. Ten infants with uncorrected CCHD and 12 infants in a control group were studied at 2 weeks of age and again at 3 months. Indirect calorimetry was used to determine REE; the doubly labeled water method was used to determine TEE and intake. At 2 weeks and 3 months of age, infants with CCHD weighed significantly less than infants in the control group. No significant difference was seen in energy intake or REE between groups during either period. TEE was slightly but not statistically increased in the CCHD group at 2 weeks (72.6 ± 17.4 vs 59.8 ± 10.9 kcal/kg/d) and significantly increased at 3 months (93.6 ± 23.3 vs 72.2 ± 13.2 kcal/kg/d,
P ≤ .03). We conclude that increased TEE but not increased REE is a primary factor in the reduced growth in infants with CCHD. (J Pediatr 1998;133:755-60)
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