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This work is based on a recent theoretical study of how the hydrostatic pressure and core/shell sizes affect the optical properties associated with the transition from the ground state to first excited state (1s–1p), of an exciton confined in spherical core/shell quantum dots (SCSQDs). We have computed under an effective mass framework, linear, third-order nonlinear, and total absorption coefficients (AC) and refractive index (RI) as functions of photon energy for different sizes of SCSQDs with varying hydrostatic pressure. Our results show that the optical absorption is deeply dependent on the incident light intensity. Both AC and RI significantly influenced by the confinement and pressure effects.
The link between circulating glucocorticoids and leptin in beef calves has not been explored but has been noted in several studies. The aim of this study is to determine the effects of exogenous glucocorticoids given at birth and 1 day of age on serum leptin concentrations in beef calves. Ruminant animals secrete leptin, which is thought to be important for the programming of the hypothalamic appetite centers. Angus crossbred cows (n = 31) bred via natural service were utilized for this experiment. At parturition (day 0), calf BW was recorded and each calf was infused intravenously with either a hydrocortisol sodium succinate solution (HC, 8 males and 8 females) at a dosage of 3.5 μg/kg of BW or a similar volume of saline solution (CONT, 7 males and 8 females). Each calf was given a second infusion of its respective treatment 24 h postpartum at 1.5 μg/kg of BW for HC treatment. Calf treatment was blocked by sex, dam body condition score (BCS), and dam age. Blood samples were taken via jugular venipuncture before infusion, daily from days 0 to 5, then every other day up to day 17. Serum leptin and cortisol concentrations were analyzed via radioimmunoassay. Dam age, dam BCS, calf BW, and serum leptin and cortisol concentrations were analyzed using MIXED procedure of SAS. Dam age was not different (P = 0.81) among HC and CONT calves (4.9±0.5 and 4.7±0.5, respectively). Dam BCS was not different between treatments (5.7±0.2 and 5.6±0.2 HC and CONT, respectively; P = 0.66). There was no difference in calf birth BW between treatments (P = 0.87) and averaged 38.3±1.4 kg. Cortisol concentrations were not different between both treatments (P = 0.23) from birth to day 4 of age. Calves that received the HC treatment showed significantly reduced (P = 0.03) leptin concentrations on days 1 to 13. Calf BW from 60 to 150 days of age was not different between CONT and HC treated calves (P = 0.65). These data indicate that exogenous glucocorticoids can be used to suppress neonatal leptin levels in calves. This could lead to changes in voluntary feed intake of treated calves.
We have studied the effect of hydrostatic pressure on the confined exciton in a spherical core–shell quantum dot. Using a simple variational approach under the framework of effective mass approximation, we have computed the excitonic binding energy as a function of the shell thickness under the applied hydrostatic pressure. Our results show that the ground state binding energy of exciton depends greatly on the shell thickness, which tends to the two-dimensional limit of 4RX, when the ratio a/b tends to unity. The numerical calculations also suggest that the applied hydrostatic pressure favors the attraction between electrons and holes so the excitonic binding energy increases when pressure increases.
The aim of this study is to determine the effects of early and mid-gestation nutrient restriction on maternal metabolites and foetal growth. Primiparous Angus cows were synchronized and inseminated with semen from one sire. Dietary treatments were: control to gain 1 kg/week (CON) or 0.55% maintenance energy and CP requirements (nutrient restricted; NR). A subset of dams was fed NR (n=8) or CON (n=8) from days 30 to 110 of gestation. Another group was fed CON (n=8), days 30 to 190; NR (n=7), days 30 to 110 followed by CON days 110 to 190; or CON, (n=7) days 30 to 110 followed by NR days 110 to 190. Cows were harvested at days 110 or 190 of gestation, when foetal measurements and samples were collected. Cows that were NR during days 30 to 110 or 110 to 190 of gestation lost significant BW and body condition score (P<0.001), this was associated with reduced plasma glucose during NR (P<0.002). Foetal weights, empty foetal weights, abdominal and thoracic circumferences were all reduced (P<0.03) in day 110 NR animals. Foetal perirenal adipose as a percentage of empty foetal weight was increased (P=0.01) in NR day 110 female foetuses compared with CON foetus. Maternal serum triglycerides at day 110 of gestation were decreased (P<0.05) in NR dams, whereas foetal serum triglycerides were increased (P<0.05) in response to maternal NR. Foetal weights tended to be reduced (P=0.08) in NR/CON and CON/NR v. CON/CON cattle at day 190 of gestation. Empty foetal weights, abdominal and thoracic circumferences were reduced (P⩽0.03) in NR/CON and CON/NR v. CON/CON cattle. Brain weight as a percentage of empty foetal weight was increased (P<0.001) in NR/CON and CON/NR v. CON/CON cattle. Foetal perirenal adipose as a percentage of empty foetal weight was increased (P=0.003) in NR/CON and CON/NR v. CON/CON cattle. Maternal serum triglycerides at day 190 of gestation were decreased (P<0.05) in association with maternal NR. Foetal serum triglycerides at day 190 of gestation were increased (P<0.05) in response to maternal NR during early gestation but decreased by NR in mid gestation compared with CON foetuses. The data show that maternal nutrient restriction during early or mid-gestation cause’s asymmetrical foetal growth restriction, regardless if the restriction is preceded or followed by a period of non-restriction.
The Earth is within the Contemporaneous Solar Maximum (CSM), analogous to the Medieval Solar Maximum (MSM). If this analogy is valid, solar activity will continue to increase well into the 21st century. We have completed 75 single-ring and 10 double-ring measurements from ad 1065 to ad 1150 to obtain information about solar activity during this postulated analog to solar activity during the MSM. δ14C decreases steadily during the period ad 1065 to ad 1150 but with cyclical oscillations around the decreasing trend. These oscillations can be successfully modeled by four cycles. These four frequencies are 1/52 yr-1, 1/22 yr-1, 1/11 yr-1, and 1/5.5 yr, i.e., the 4th harmonic of the Suess cycle, the Hale and Schwabe cycles and the 2nd harmonic of the Schwabe cycle.
Audiometric tests do not adequately reflect the hearing handicap experienced by individuals with hearing loss and account for only part of the variance in hearing handicap perceptions (Weinstein & Ventry, 1983). The present study investigates the relationship between degree of hearing impairment, psychosocial factors and hearing handicap in a New Zealand war veteran sample. Forty-seven veterans (Mean age = 77.51, SD = 5.99) with some degree of hearing impairment completed a questionnaire which included the Hearing Handicap Inventory (HHI) (Newman et al., 1990), the SF36 sub-scales for general health and mental health (Ware, Kosinski & Keller, 1994), questions relating to hearing aid use and demographic details. Audiometric test information for each veteran was accessed through the national war pensions organisation. Analyses revealed no significant relationship between percentage hearing loss and perceptions of hearing handicap. Those who reported lower satisfaction with their hearing aids, those in poorer physical health and those who had been using hearing aids for a longer time reported higher scores on the HHI. These findings suggest that aspects of the rehabilitation process are important factors in the individual's experience of hearing handicap and that non-auditory factors (such as general health) may be essential considerations in this process.
Triple supermassive black holes (SMBH) can form during the hierarchical mergers of massive galaxies with an existing binary. Perturbations by a third black hole may accelerate the merging process of an inner binary, for example through the Kozai mechanism. We analyze the evolution of simulated hierarchical triple SMBHs in galactic centers, and find resonances in the evolution of the semi-major axis, the eccentricity and the inclination, for both the inner and the outer orbits of the triple system, which are not only Kozai like. Through resonant oscillations, SMBH can trigger a significant increase of the inner SMBH binary eccentricity shortening the merger timescale expected from gravitational wave (GW) emission. As hierarchical triple SMBHs may be frequent in massive galaxies, the influence of orbital resonances is of great importance to our understanding of black hole coalescence and gravitational wave detection. Although Kozai mechanism is believed to play an important role in this process, detailed studies on the pattern of these resonances is necessary.
Affordable, high quality SiC wafers are very desirable for a variety of new technologies including GaN based lighting, RF, and high-power electronics based on wide band gap materials. At Litton Airtron we have a major effort in the growth and characterization of SiC. We will present data on 35, 50 and 75-mm diameter crystals. We are growing both n-type, semiinsulating 4H, 6H, and 15R material. A variety of characterization techniques are being used at Litton Airtron to determine wafer quality. These include Raman microscopy, digital wafer photography, and crossed polarizer images. Raman spectroscopy is an excellent probe of polytype and carrier concentration for n-type materials; in addition it can be done at room temperature and is sufficiently fast that it can be used in an industrial environment. The use of digital photography allows for the collection of images that can be quantitatively analyzed and archived.
Evidence for a new microcrystalline precipitate in CZ Si annealed for 256 hrs at 635°C is presented by electron microdiffraction. This may be a precursor phase for the formation of amorphous platelets . Multiple scattering microdiffraction calculations which distinguish the symmetries of two models for the thermal donor are also given.
The pulsed-laser induced photochemical production of metallic Ga islands on the surface of GaAs cleaved, irradiated, and studied in ultrahigh vacuum (UHV) is documented through photoelectron spectroscopy and subsequent scanning electron microscopy. Ga islands are detected for laser fluences as low as 1 mJ/cm2, far below those previously reported for modification of GaAs, and for which the temperature rise is negligible.
The technique of high resolution electron microscopy has been used to examine the structure of several multilayer systems (MLS) on an atomic scale. Mo/Si multilayers, in use in a number of x-ray optical element applications, and Mo/Si multilayers, of interest because of their magnetic properties, have been imaged in cross-section. Layer thicknesses, flatness and smoothness have been analysed: the layer width can vary by up to 0.6nm from the average value, and the layer flatness depends on the quality of the substrate surface for amorphous MLS, and on the details of the crystalline growth for the crystalline materials. The degree of crystallinity and the crystal orientation within the layers have also been investigated. In both cases, the high-Z layers are predominantly crystalline and the Si layers appear amorphous. Amorphous interfacial regions are visible between the Mo and Si layers, and crystalline cobalt suicide interfacial regions between the Co and Si layers. Using the structural measurements obtained from the HREM results, theoretical x-ray reflectivity behaviour has been calculated. It fits the experimental data very well.
We report the chemical synthesis of Fe-core/Au-shell nanoparticles (Fe/Au) by a reverse micelle method, and the investigation of their growth mechanisms and oxidation-resistant characteristics. The core-shell structure and the presence of the Fe and Au phases have been confirmed by transmission electron microscopy, energy dispersive spectroscopy, x-ray diffraction, Mössbauer spectroscopy, and inductively coupled plasma techniques. Additionally, atomic-resolution Z-contrast imaging and electron energy loss spectroscopy in a scanning transmission electron microscope have been used to study details of the growth processes. The Au-shells grow by nucleating on the Fe-core surfaces before coalescing. First-order reversal curves, along with the major hysteresis loops of the Fe/Au nanoparticles have been measured as a function of time in order to investigate the evolution of their magnetic properties. The magnetic moments of such nanoparticles, in the loose powder form, decrease over time due to oxidation. The less than ideal oxidation-resistance of the Au shell may have been caused by the rough Au surfaces. In a small fraction of the particles, off-centered Fe cores have been observed, which are more susceptible to oxidation. However, in the pressed pellet form, electrical transport measurements show that the particles are fairly stable, as the resistance and magnetoresistance of the pellet do not change appreciably over time. Our results demonstrate the complexity involved in the synthesis and properties of these heterostructured nanoparticles.
The effect of the laser energy density used to deposit Bi onto amorphous aluminum oxide (a-Al2O3) on the growth of Bi nanocrystals has been investigated using transmission electron microscopy of cross section samples. The laser energy density on the Bi target was varied by one order of magnitude (0.4 to 5 J cm-2). Across the range of energy densities, in addition to the Bi nanocrystals nucleated on the a-Al2O3 surface, a dark and apparently continuous layer appears below the nanocrystals. Energy dispersive X-ray analysis on the layer have shown it is Bi rich. The separation from the Bi layer to the bottom of the nanocrystals on top is consistent with the implantation range of Bi species in a-Al2O3. As the laser energy density increases, the implantation range has been measured to increase. The early stages of the Bi growth have been analyzed in order to determine how the Bi implanted layer develops.
Spectra of photoelectrons and thermionic electrons emitted from silicon during pulsed laser irradiation at energy densities encompassing the thresholds for laser annealing and damage are reported. Annealing is accomplished with a 90-nsec pulse of 532-nm light, which may be accompanied by a 266-nm probe pulse. A cylindrical mirror analyzer is used for energy resolution of emitted electrons. Time-resolved reflectivity at 633 nm verifies attainment of the high-reflectivity annealing phase. Spectral widths and total yields imply a modest electron temperature (T < 3000 K) during annealing. The data suggest that the work function of the silicon (111) face may increase about 0.6 eV upon transition to the molten phase.
Amorphous d.c. sputtered SbOx films (0.19< x<2.0) have been found to be fast crystallising materials sensitive to nano- and pico-second laser pulses, and have potential applications as optical data-storage media. They were crystallised in-situ in a JEOL 4000EX TEM, and the crystallisation recorded onto video tape. The crystallisation of the SbO0.37 films occurred by random nucleation followed by growth until coalescence. In contrast the crystallisation of the SbO0.533 films occurred by surface crystallisation across the whole film followed by bulk crystallisation through the film, during which contrast in the TEM increased steadily. Analysing the video frames in an image processing package enabled kinetic parameters such as transformation index and activation energy to be extracted. High resolution transmission electron microscopy showed the crystalline phase to contain nano-crystallites approximately 10 nm in size in a less-ordered matrix.
Solvothermal/hydrothermal reactions of 4, 4′-biphenyldicarboxylic acid (H2bpdc) and cobalt (II) salt with pyridine derivative ligands such as 3-methylpyridine (3-pic), 4-methylpyridine (4-pic), as well as a longer terminal ligand 4-benzylpyridine (4-bzpy) generated four new extended structures: 1D zigzag polymer chain 1 crystallized in C2/c with a formula [Co(bpdc)(3-pic)2]·(3-pic); 1D helical chain compound 2 crystallized in P41 with a formula [Co(bpdc)(4-pic)2], 2D non-interpenetrating network 3 crystallized in P2221 with a formula [Co(bpdc)(4-pic)2]·(4-pic)0.5·H2O, and 2D non-interpenetrating network 4 crystallized in P2/c, formulated as [Co(bpdc)(bzpy)2]. Our studies show that terminal ligands play an important role in affecting the dimensionality and topology of the structures formed. Magnetic susceptibility and isothermal magnetization results revealed an antiferromagnetic ground state for 3 with a transition temperature T = 4.7 K, and paramagnetic behavior at high temperature range for 1 and 2.
Educational and psychological research over the last decade has consistently supported the presupposition that learning is a dynamic process in which knowledge and motivation work in concert to influence achievement (Alexander, 1997; Pintrich et al., 1993; Tanaka and Yamauchi, 2001). Research by Schommer (e.g., 1990, 1993) and others (e.g., Hofer, 2000; Kardash and Scholes, 1996; King and Kitchener, 1994) has also shown that students’ beliefs about knowledge and the process of knowing (i.e., epistemology) play powerful roles in their learning and development. In addition, it is now understood that constructs like knowledge, motivation, and epistemology are multidimensional and make unique contributions to the learning process (e.g., Alexander, 1997; Buehl et al., 2002; Middleton and Midgley, 1997; Schommer, 1990). For example, research investigating goal orientations in ninth-grade students has shown that avoidance-oriented goals are correlated with higher test anxiety, while performance-oriented goals are related to lower self-efficacy (Niemivirta, 2002). Additional studies suggest that these relations may vary according to developmental levels. Whereas learning or mastery goals relate to both “higher levels of content knowledge and better grades” among middle school students (Gehlbach, 2006, p. 366), the process becomes more differentiated in college. Specifically, performance goals consistently correlate with grades while learning goals appear to be more closely aligned with student interest (Harackiewicz et al., 2005).
We report on XMM-Newton and Chandra observations of the globular cluster NGC 2808. We detect one quiescent low mass X-ray binary of the 3±1 expected, if these systems are formed through encounters, and we show evidence for the presence of 20±10 bright cataclysmic variables in the core with a luminosity above 4×1031 erg s−1. We also review the specific nature of cataclysmic variables in globular clusters with reference to recent VLT/FORS1 observations of a cataclysmic variable in M 22.
Mathematical programming-based systems analysis is used to examine the consequences of alternative operation configuration for the agricultural operations within the Texas Department of Criminal Justice. Continuation versus elimination of the total operation as well as individual operating departments are considered. Methodology includes a firm systems operation model combined with capital budgeting and an integer programming based investment model. Results indicate the resources realize a positive return as a whole, but some enterprises are not using resources profitably. The integer investment model is found to be superior for investigating whether to continue multiple interrelated enterprises.
Centrally administered glucagon-like peptide-1 (GLP-1) inhibits feeding in fasted rats, but its role in human satiety has been largely unexplored. The present study investigated the effect of peripheral GLP-1 infusion on gastric emptying and satiety in man. Ten non-obese male subjects were infused in a randomized single-blind within-subject crossover study using saline infusion as control. They received either a GLP-1 infusion (1·2 pmol/kg per min) or a saline infusion for 1 h, at 18.00 hours. At 20 min after starting the infusion the gastric emptying of a 400 ml water load was measured. Subjects completed behavioural self-rating scales to assess hunger and satiety. After 40 min subjects were given a buffet meal ad libitum and their food intake was recorded. GLP-1 infusion raised circulating GLP-1 concentrations to approximately twice those seen following a meal. It did not affect circulating insulin levels but caused a small fall in glucose levels. Gastric emptying of the water load was significantly delayed by the GLP-1 infusion. Energy intake from the buffet was unaffected by GLP-1 infusion. Self-assessment of hunger and satiety was similarly unaffected by the infusion before the buffet meal, although subjects tended to be less hungry after the buffet meal following GLP-1 infusion (P < 0·09). GLP-1 infusion delayed gastric emptying but had a minimal effect on food intake and satiety. This study casts doubts on whether GLP-1 is a major satiety factor in man, although a raised circulating plasma glucose level, as would normally occur postprandially, might be necessary for GLP-1 to increase satiety.