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101.
102.
Starting-up of photovoltaic (PV) inverters involves pre-charging of the input dc bus capacitance. Ideally, direct pre-charging of this capacitance from the PV modules is possible as the PV modules are current limited. Practically, the parasitic elements of the system such as the PV module capacitance, effective wire inductance and resistance determine the start-up transient. The start-up transient is also affected by the contactor connecting the PV modules to the inverter input dc bus. In this work, the start-up current and voltages are measured experimentally for different parallel and series connections of the PV modules. These measurements are used to estimate the stray elements, namely the PV module capacitance, effective inductance and resistance. The estimation is based on a linear small-signal model of the start-up conditions. The effect of different connections of the PV modules and the effect of varying irradiation on the scaling of the values of the stray elements are quantified. The System model is further refined by inclusion of connecting cable capacitance and contactor resistance. Dynamics of the resulting fifth-order model are seen to be consistent with those of the simplified third-order model. The analysis of this paper can be used to estimate the expected peak inrush current in PV inverters. It can also be used to arrive at a detailed modelling of PV modules to evaluate the transient behaviour. 相似文献
103.
Heather M. Alger Maricel V. Maffini Neesha R. Kulkarni Erin D. Bongard Thomas Neltner 《Comprehensive Reviews in Food Science and Food Safety》2013,12(1):90-119
Food additives and substances considered “generally recognized as safe” must not be allowed in food unless there is a reasonable certainty in the minds of competent scientists that the substance is not harmful under the intended conditions of use. Scientists determine safety by ensuring that the expected exposure is less than the acceptable daily intake. The U.S. Food and Drug Administration (FDA) provides guidance documents to assist safety assessors in this analysis. A November 2011 workshop sponsored by The Pew Charitable Trusts, the Institute of Food Technologists, and the journal Nature reviewed the agency's exposure assessment approaches. More than 70 experts from government (including FDA), industry, academia, and public interest organizations examined the principles underlying dietary exposure assessments for substances added to human food, and responded to questions about current methods. FDA's approach was seen as serving the agency reasonably well, but participants identified opportunities for improvement. Although reaching a consensus was not a goal, general agreements emerged that FDA should develop a science‐based framework to prioritize and reassess prior safety decisions, and conduct more extensive postmarket monitoring. Participants discussed the possibility of harmonizing different approaches to assess dietary exposure. They generally agreed that collaboration, communication, and exchanging scientific information between agencies and stakeholders would help assessors use the most current information to make better decisions. Participants identified data gaps and opportunities to fill the gaps using new tools and technologies. Participants generally agreed on the need to consider all dietary sources in a cumulative dietary exposure assessment. 相似文献
104.
A khoa variety popularly known as Danedar khoa, which has a very short life under ambient conditions, was studied for its shelf life at room and refrigerated temperatures under controlled conditions after packaging in a flexible material (poster paper/aluminium foil/low-density polyethylene [LDPE]). The samples were observed periodically for characteristics such as moisture content, peroxide value, titratable acidity and overall acceptability. Samples packed under nitrogen and stored under refrigeration were found to be distinctly superior in all respects. 相似文献
105.
Anu Bajaj Atul Khanna Narendra K. Kulkarni Suresh K. Aggarwal 《Journal of the American Ceramic Society》2009,92(5):1036-1041
Bismuth borate glasses from the system: 40Bi2 O3 –59B2 O3 –1Tv2 O3 (where Tv=Al, Y, Nd, Sm, and Eu) and three glasses of composition: 40Bi2 O3 –60B2 O3 , 37.5Bi2 O3 –62.5B2 O3 and 38Bi2 O3 –60B2 O3 –2Al2 O3 were prepared by melt quenching and characterized by density, UV-visible absorption spectroscopy and differential thermal analysis (DTA) studies. Bismuth borate glasses exhibit a very strong optical absorption band just below their absorption edge. Glasses were devitrified by heat treatment at temperatures above their glass transition temperatures and the crystalline phases produced in them were characterized by Fourier transform infrared (FTIR) absorption spectroscopy and X-ray diffraction (XRD). Bi3 B5 O12 was found to be the most abundant phase in all devitrified samples. DTA studies on glasses and FTIR and XRD analysis on crystallized samples revealed that very small amounts of trivalent ion doping causes significant changes in the devitrification properties of bismuth borate glasses; rare-earth ions promote the formation of metastable BiBO3 –I and BiBO3 –II phases during glass crystallization. 相似文献
106.
107.
R. S. Dutta S. Majumdar P. K. Limaye U. D. Kulkarni G. K. Dey 《Transactions of the Indian Institute of Metals》2011,64(1-2):31-36
Ni-Cr-Fe based superalloy 690 substrate, pack aluminized at 1273 K, revealed formation of multilayer comprising (NiCr)Al + Cr5Al8, Ni2Al3 + Cr5Al8, NiAl and γ phases. Knoop hardness number varied from 225 to 1142 along the cross-section. Wear and friction tests on aluminized specimen were performed in dry medium using reciprocating sliding wear and friction machine with tungsten carbide ball at 15 N load with frequencies at 10, 15 and 20 Hz. The coefficient of friction, the static ones were obtained in the vicinity of 0.2, 0.3 and 0.5, while dynamic ones were 0.3, 0.4 and 0.4 respectively. For the ball, the wear rate was 1.9 × 10?6, 1.2 × 10?5 and 1.5 × 10?5 mm3/Nm, whereas the wear rate was 5.8 × 10?5, 3.8 × 10?4 and 4.6 × 10?4 mm3/Nm respectively for the aluminized specimen indicating good adherent surface coating. 相似文献
108.
Stayton P.S. Hoffman A.S. El-Sayed M. Kulkarni S. Shimoboji T. Murthy N. Bulmus V. Lackey C. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》2005,93(4):726-736
Many molecular imaging techniques rely on tracer methods to visualize specific physiological processes in cells, animals, and humans. A new family of "smart" delivery systems for biomolecules has opened new opportunities for the molecular imaging field. One class of polymeric carriers reversibly become membrane destabilizing in response to sharp pH changes and were designed for delivering proteins and nucleic acids to intracellular compartments. These carriers could enable the use of imaging agents and intracellular reporters whose site of action made them previously inaccessible. A second class of stimuli-responsive polymer-biomolecule conjugates can be reversibly formed into particles of closely defined sizes. The ability to control when and where the protein or DNA species is in the free versus particle form may allow imaging applications that exploit their differential size and diffusion properties. 相似文献
109.
Creep analysis of orthotropic rotating disks with variable thickness has been carried out for secondary stage of creep. Norton's power law of creep is employed to derive general expressions for stresses and strain rates in the disks. These expressions have been utilized to find stress and strain rate distributions for disks with the following types of thicknesses - (i) constant thickness, (ii) linearly varying thickness, and (iii) hyperbolically varying thickness. The numerical computations to study the effects of anisotropy and the profile of the disks on stresses and strains have been carried out employing the method of successive approximations. Five different cases of anisotropy have been considered. Selecting a certain type of material anisotropy and an optimum profile for the disk may result in a better design for the turbine disks. 相似文献
110.
Visweswariah K. Kulkarni S.R. Verdu S. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1998,44(2):462-471
A random number generator generates fair coin flips by processing deterministically an arbitrary source of nonideal randomness. An optimal random number generator generates asymptotically fair coin flips from a stationary ergodic source at a rate of bits per source symbol equal to the entropy rate of the source. Since optimal noiseless data compression codes produce incompressible outputs, it is natural to investigate their capabilities as optimal random number generators. We show under general conditions that optimal variable-length source codes asymptotically achieve optimal variable-length random bit generation in a rather strong sense. In particular, we show in what sense the Lempel-Ziv (1978) algorithm can be considered an optimal universal random bit generator from arbitrary stationary ergodic random sources with unknown distributions 相似文献