Quantitative Thermal Microscopy Measurement with Thermal Probe Driven by dc+ac Current

Quantitative thermal measurements with spatial resolution allowing the examination of objects of submicron dimensions are still a challenging task. The quantity of methods providing spatial resolution better than 100 nm is very limited. One of them is scanning thermal microscopy (SThM). This method is a variant of atomic force microscopy which uses a probe equipped with a temperature sensor near the apex. Depending on the sensor current, either the temperature or the thermal conductivity distribution at the sample surface can be measured. However, like all microscopy methods, the SThM gives only qualitative information. Quantitative measuring methods using SThM equipment are still under development. In this paper, a method based on simultaneous registration of the static and the dynamic electrical resistances of the probe driven by the sum of dc and ac currents, and examples of its applications are described. Special attention is paid to the investigation of thin films deposited on thick substrates. The influence of substrate thermal properties on the measured signal and its dependence on thin film thermal conductivity and film thickness are analyzed. It is shown that in the case where layer thicknesses are comparable or smaller than the probe–sample contact diameter, a correction procedure is required to obtain actual thermal conductivity of the layer. Experimental results obtained for thin SiO\(_{\mathrm {2}}\) and BaTiO\(_{\mathrm {3 }}\)layers with thicknesses in the range from 11 nm to 100 nm are correctly confirmed with this approach.     

Space charge accumulation in two power cable grades of XLPE

The accumulation of space charge in XLPE (cross-linked polyethylene), cross-linked using DCP (dicumyl peroxide) or a silane-based grafting process, was studied via the LIPP (laser-induced-pressure-pulse) technique. Planar samples 0.5 mm thick were obtained from the XLPE insulation of power distribution cables. DC fields to 10 kV/mm were applied at temperatures in the range 20 to 90°C. Usually the DCP samples developed heterocharge, and the silane samples homocharge. However, the observed space charge densities were not very different. Nearly all of the charge accumulated within 100 μm of each electrode, with very little in the remainder of the volume. Both sample types showed a near-perfect inversion of the equilibrium space charge profiles on reversing the applied voltage polarity. This observation is explained in terms of charge injection at the electrodes, electron transfer between electrode and XLPE in either direction involving the same narrow `window' of combined donor and acceptor states in the insulator, centered on the Fermi level     

Development of a Cup Burner Apparatus for Fire Suppression Evaluation of High-Expansion Foams

We developed a bench-scale high-expansion aqueous foam generator and integrated it into a traditional cup burner apparatus. Foam expansion ratios ranging from 50:1 to 590:1 could be achieved using air flow rates from 16 l/min to 38 l/min and liquid foam solution flow rates of 50 ml/min to 140 ml/min. The flow rates, foam expansion ratios, and cup burner flame extinction behavior with nitrogen provide a suitable bench-scale platform for controlled, systematic investigations of foam/flame interactions for a range of foam properties. Foams with an expansion ratio of 200:1 contain 81% water by mass. When evaporated completely, this amount of water should be insufficient to extinguish propane flames in oxidizer streams with 60% oxygen based on extinction of these flames by water mist. However, the 200:1 foam easily extinguishes a propane flame even in 100% oxygen.     

Maximum exergy input rate from a hot stream in solar‐driven refrigerators

The authors believe that reducing the size of solar‐driven refrigerators and air conditioning systems will make them more attractive to potential users. This paper presents a contribution to understanding the behaviour of such systems with a view to determining the manner in which refrigeration rate, mass flows and heat transfer areas are related. The intention is to make possible the identification of preliminary design rules. The basic thermodynamic problem of how to obtain maximum exergy input rate in a solar‐driven refrigerator is considered. The existence of an optimal refrigerant flow rate for maximum refrigeration is investigated. The analysis proceeds by relating the entropy generation rate, the physical and operating parameters, and the constraints of the system, through well‐established heat transfer relationships. Finally, a thermodynamic analysis determines the optimal characteristics that lead to minimum entropy generation. The second law efficiency is identified as the appropriate figure of merit for the thermodynamic optimum. Copyright © 2001 John Wiley & Sons, Ltd.     

Excited State Structural Dynamics of the Charge Transfer State of Peridinin

We present infrared and visible transient absorption measurements of the first excited singlet state (S₁ and S_1/ICT) of peridinin in methanol, isopropanol, and chloroform solution following one-photon excitation, using 490 nm light, to excite the S₂ state that populates S₁ via rapid (∼50 fs in methanol) internal conversion. This technique enables the study of subsequent structural dynamics in S₁ involved in the formation of the charge transfer state. The S₁ lifetime of peridinin in methanol, isopropanol, and chloroform is found to be 12, 54, and 65 ps, respectively, as determined by infrared transient absorption. We observe two formation timescales in the S₁ state. We attribute the shortest timescale to relaxation following internal conversion and the longer timescale to formation of the S_1/ICT state.     

Evidence of space-charge effects in thermal poling

The in situ thermal poling processes in germanosilicate fibers for positive and negative poling voltages are significantly different. Thermal poling of silica fibers consists of two processes: the faster linear process of charge migration and the subsequent single exponential process of charge ionization. Both the shielding electrical field due to charge migration and the ionization electrical field due to charge ionization are able to be frozen-in at room temperature and lead to the residual linear electrooptic effects. The observations support that the mechanism of the induced electrooptic effects is based on space charge electrical fields instead of dipole/bond orientation     

Provider feedback to improve 5A's tobacco cessation in primary care: a cluster randomized clinical trial.

The electronic health record (EHR) may be an effective tool to help clinicians address tobacco use more consistently. To evaluate the impact of EHR-generated practice feedback on rates of referral to a state-level tobacco quitline, we conducted a cluster randomized clinical trial (feedback versus no feedback) within 19 primary care clinics in Oregon. Intervention clinics received provider-specific monthly feedback reports generated from EHR data. The reports rated provider performance in asking, advising, assessing, and assisting with tobacco cessation compared with a clinic average and an achievable benchmark of care. During 12 months of follow-up, EHR-documented rates of advising, assessing, and assisting were significantly improved in the intervention clinics compared with the control clinics (p<.001). A higher case-mix index and presence of a clinic champion were associated with higher rates of referral to a state-level quitline. EHR-generated provider feedback improved documentation of assistance with tobacco cessation. Connecting physician offices to a state-level quitline was feasible and well accepted.     

Plasticity in the maternal circuit: Effects of experience and partum condition on brain astroctye number in female rats.

Female rats that have received a maternal experience undergo enhanced c-fos expression in a number of brain sites when reexposed to pups. The present 2 studies examined changes in the expression of another brain protein, glial fibrillary acidic protein (GFAP), which is a major unit of the astrocytic cytoskeleton. In both experiments, primiparous and multiparous female rats were given varying amounts of postpartum contact with pups and overdosed after varying intervals, with no pups. Brains were prepared for GFAP immunohistochemical analysis. In both studies, Day 5 postpartum multiparous subjects given additional postpartum contact with pups, when compared with pup-exposed primiparous subjects, were found to have significantly higher numbers of GFAP positive cells in the medial preoptic area of the hypothalamus, an area critical for the expression of maternal behavior, but not in control sites. In Experiment 2, an opposite effect of parity was found in the medial amygdala and habenula. (PsycINFO Database Record (c) 2010 APA, all rights reserved)