2,189 research outputs found
Thermoplastic deformation of silicon surfaces induced by ultrashort pulsed lasers in submelting conditions
A hybrid 2D theoretical model is presented to describe thermoplastic
deformation effects on silicon surfaces induced by single and multiple
ultrashort pulsed laser irradiation in submelting conditions. An approximation
of the Boltzmann transport equation is adopted to describe the laser
irradiation process. The evolution of the induced deformation field is
described initially by adopting the differential equations of dynamic
thermoelasticity while the onset of plastic yielding is described by the von
Mise's stress. Details of the resulting picometre sized crater, produced by
irradiation with a single pulse, are then discussed as a function of the
imposed conditions and thresholds for the onset of plasticity are computed.
Irradiation with multiple pulses leads to ripple formation of nanometre size
that originates from the interference of the incident and a surface scattered
wave. It is suggested that ultrafast laser induced surface modification in
semiconductors is feasible in submelting conditions, and it may act as a
precursor of the incubation effects observed at multiple pulse irradiation of
materials surfaces.Comment: To appear in the Journal of Applied Physic
Etched graphene quantum dots on hexagonal boron nitride
We report on the fabrication and characterization of etched graphene quantum
dots (QDs) on hexagonal boron nitride (hBN) and SiO2 with different island
diameters. We perform a statistical analysis of Coulomb peak spacings over a
wide energy range. For graphene QDs on hBN, the standard deviation of the
normalized peak spacing distribution decreases with increasing QD diameter,
whereas for QDs on SiO2 no diameter dependency is observed. In addition, QDs on
hBN are more stable under the influence of perpendicular magnetic fields up to
9T. Both results indicate a substantially reduced substrate induced disorder
potential in graphene QDs on hBN
High-Tc bolometers with silicon-nitride spiderwebsuspension for far-infrared detection
High-Tc GdBa2Cu3O7-ÎŽ (GBCO) superconducting transition edge bolometers with operating temperatures near 90 K have been made with both closed silicon-nitride membranes and patterned silicon-nitride (SiN) spiderweb-like suspension structures. As a substrate silicon-on-nitride (SON) wafers are used which are made by fusion bonding of a silicon wafer to a silicon wafer with a silicon-nitride top layer. The resulting monocrystalline silicon top layer on the silicon-nitride membranes enables the epitaxial growth of GBCO. By patterning the silicon-nitride the thermal conductance G is reduced from about 20 to 3 ÎŒW/K. The noise of both types of bolometers is dominated by the intrinsic noise from phonon fluctuations in the thermal conductance G. The optical efficiency in the far infrared is about 75% due to a goldblack absorption layer. The noise equivalent power NEP for FIR detection is 1.8 pW/âHz, and the detectivity D* is 5.4Ă1010 cm âHz/W. Time constants are 0.1 and 0.6 s, for the closed membrane and the spiderweb like bolometers respectively. The effective time constant can be reduced with about a factor 3 by using voltage bias. Further reduction necessarily results in an increase of the NEP due to the 1/f noise of the superconductor
Effects of environmental enrichment on behavioral responses to novelty, learning, and memory, and the circadian rhythm in cortisol in growing pigs
Previously we showed that pigs reared in an enriched environment had higher baseline salivary cortisol concentrations during the light period than pigs reared under barren conditions. In the present experiment, it was investigated whether these higher baseline salivary cortisol concentrations were a real difference in cortisol concentration or merely represented a phase difference in circadian rhythm. The effects of different cortisol concentrations on the behavioral responses to novelty and learning and long-term memory in a maze test were also studied in enriched and barren housed pigs. At 9 weeks of age enriched and barren housed pigs did not differ in baseline salivary cortisol concentrations nor in circadian rhythm, but at 22 weeks of age barren housed pigs had a blunted circadian rhythm in salivary cortisol as compared to enriched housed pigs. The differences in baseline salivary cortisol concentrations between enriched- and barren-housed pigs are age-dependent, and become visible after 15 weeks of age. Enriched- and barren-housed piglets did not differ in time spent on exploration in the novel environment test. Barren-housed pigs had an impaired long-term memory in the maze test compared to enriched-housed pigs; however, no differences in learning abilities between enriched- and barren-housed pigs were found. Because blunted circadian cortisol rhythms are often recorded during states of chronic stress in pigs and rats or during depression in humans, it is suggested that the blunted circadian rhythm in cortisol in barren-housed pigs similarily may reflect decreased welfare.
Analysing the effects of travel information on public transport travellerâs decision making and learning
This thesis examines the effect of travel information on a public transport travellerâs decision making over time. It investigates whether the effect of information is sustained over time and is affected by its type and reliability. It is postulated that the traveller will attain better decision outcomes over time, and this process is reinforced when given information. It is postulated that dynamic information would produce the best outcomes, followed by static information and no information. A series of computer-based experiments, in which the participants made hypothetical trips by public bus under various travel information and operating conditions, were conducted. At the aggregate level, the hypothesised relationships are not observed at a statistically significant level. At the disaggregate level, day-to-day decisions are shown to relate significantly to the outcome of the previous day, with the participant more likely to seek a more rewarding but riskier choice if the previous day sees no adverse outcome, and vice-versa. When the information is static, decision changes are few and incremental. When it is dynamic, these changes are more frequent and pronounced, with choices âanchoredâ around values provided by the information. Nonetheless, a significant proportion of participants made no or few changes, regardless of information or operating conditions. The findings suggest a higher propensity for some travellers to use dynamic information over static information over time, regardless of reliability. On the other hand, those who acquire information do not necessarily maximise their utility, implying that they do so for other less quantifiable factors. The benefits of information provision could also be further circumscribed by the heterogeneity of responses. This set of findings suggests that assuming travellers respond to information in a utility-maximising and homogeneous manner may over-estimate the effect of information
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