1,845 research outputs found
Analysis of the Causes and Recommendations on Elimination of Biological Damage of Structures During the Repair and Reconstruction of the State Biological Museum in Moscow
The article presents the results of mycological research on buildings of the State Biological Museum located in Moscow. The problems have been considered as for a complex of buildings of the State Biological Museum built in the late nineteenth century which, to the present time, has been operated almost in its original form. Over time, the building maintenance conditions have worsened, in particular because of construction of high-rise buildings in the immediate vicinity of the museum, as well as construction of a greenhouse above the underground passage tunnel between buildings 1 and 2. Over the years, the temperature gradients, high humidity, wear and damage of wall waterproofing and foundations have caused leaks in the underpass tunnel and the biological corrosion of stone, wood and metal structures in indoor exhibition halls. In this connection, part of the survey was to determine the types and size of biological lesions in structures, determination of the causes of biological damage, and the development of measures to eliminate the mycological problems during repair and reconstruction works in the museum
A New Quasi Resonant Dc-link For Photovoltaic Micro-inverters
PV Inverters have the task of tracking the maximum power point (MPP), and regulating the solar energy generation to this optimal operation point. The second task is the conversion of direct current produced by the solar modules into alternating current compatible with the grid. A new inverter approach such as a single phase micro inverter is emerging aimed to overcome some of the challenges of centralized inverters. As a counterpart to the central inverter, a micro inverter is a small compact module attached directly to each solar panel. To provide for the constantly increasing demand for a small size, light weight and high efficiency micro inverter, soft switching power conversion technologies have been employed. The switching stress can be minimized by turning on/off each switch when the voltage across it or the current through it is zero at the switching transition. With the addition of auxiliary circuits such as auxiliary switches and LC resonant components the so called soft switching condition can be achieved for semiconductor devices. Four main purposes to investigate the soft switching technologies for singlephase micro-inverter are: (1) to improve overall efficiency by creating the favorable operating conditions for power devices using soft-switching techniques; iv (2) to shrink the reactive components by pushing the switching frequency to a higher range with decent efficiency. (3) to ensure soft switching does not exacerbate inverter performance, meaning all conventional PWM algorithms can be applied in order to meet IEEE standards. (4) to investigate which soft switching techniques offer the cheapest topology and control strategy as cost and simple control are crucial for low power inverter applications. An overview on the existing soft-switching inverter topologies for single phase inverter technology is summarized. A new quasi resonant DC link that allows for pulse- width- modulation (PWM) is presented in this thesis. The proposed quasi resonant DC link provides zero-voltage switching (ZVS) condition for the main devices by resonating the DC-link voltage to zero via three auxiliary switches and LC components. The operating principle and mode analysis are given. The simulation was carried out to verify the proposed soft switching technique. A 150W 120VAC single-phase prototype was built. The experimental results show that the soft switching for four main switches can be realized under different load conditions and the peak efficiency can reach 95.6%. The proposed quasi DC link can be applied to both single-phase and three-phase DC/AC micro inverter. In order to boost efficiency and increase power density it is important to evaluate the power loss mechanism in each stage of operation of the micro inverter. Using the datasheet parameters of the commercially available semiconductor switches, conduction and switching losses were estimated. This thesis presents a method to analyze power losses of the new resonant DC link inverter which alleviates topology v optimization and MOSFET selection. An analytical, yet simple model for calculating the conduction and switching losses was developed. With this model a rough calculation of efficiency can be done, which helps to speed up the design process and to increase efficiency
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A behavioural approach to financial portfolio selection problem: an empirical study using heuristics
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel UniversityThe behaviourally based portfolio selection problem with investor's loss aversion and risk aversion biases in portfolio choice under uncertainty are studied. The main results of this work are developed heuristic approaches for the prospect theory and cumulative prospect theory models proposed by Kahneman and Tversky in 1979 and 1992 as well as an empirical comparative analysis of these models and the traditional mean variance and index tracking models. The crucial assumption is that behavioural features of the (cumulative) prospect theory model provide better downside protection than traditional approaches to the portfolio selection problem. In this research the large scale computational results for the (cumulative) prospect theory model have been obtained. Previously, as far as we aware, only small laboratory (2-3 arti cial assets) tests has been presented in the literature. In order to investigate empirically the performance of the behaviourally based models, a differential evolution algorithm and a genetic algorithm which are capable to
deal with large universe of assets have been developed. The speci c breeding and mutation as well as normalisation have been implemented in the algorithms. A tabulated comparative analysis of the algorithms' parameter choice is presented. The performance of the studied models have been tested out-of-sample in different conditions using the bootstrap method as well as simulation of the distribution of a growing market and simulation of the t-distribution with fat tails which characterises the dynamics of a decreasing or crisis market. A cardinality and CVaR constraints have been implemented to the basic mean variance and prospect theory models. The comparative analysis of the empirical results has been made using several criteria such as CPU time, ratio between mean portfolio return and
standart deviation, mean portfolio return, standard deviation , VaR and CVaR as alternative measures of risk. The strong in
uence of the reference point, loss aversion and risk aversion on the prospect theory model's results have been found. The prospect theory model with the reference point being the index is compared to the index tracking model. The portfolio diversi cation bene t has been found. However, the aggressive behaviour in terms of returns of the prospect theory model with the reference point being the index leads to worse performance of this model in a bearish market compared to the index tracking model. The tabulated comparative analysis of the performance of all studied models is provided in this research for in-sample and out-of-sample tests
Near-threshold production of a0(980) mesons in the reaction pp -> d K^+ \bar{K}^0
Using an effective Lagrangian approach as well as the Quark-Gluon Strings
Model we analyze near-threshold production of a0(980)-mesons in the reaction NN
-> d K \bar{K} as well as the background of non-resonant K\bar{K}-pair
production. We argue that the reaction pp -> d K^+ \bar{K}^0 at an energy
release Q<=100 MeV is dominated by the intermediate production of the
a0(980)-resonance. At larger energies the non-resonant K^+\bar{K}^0-pair
production - where the kaons are produced in a relative P-wave - becomes
important. Then effects of final-state interactions are evaluated in a
unitarized scattering-length approach and found to be in the order of a 20%
suppression close to threshold. Thus in present experiments at the Cooler
Synchrotron COSY-J\"ulich for Q<=107 MeV the a_0^+ signal can reliably be
separated from the non-resonant K^+\bar{K^0} background.Comment: 14 pages, 12 figures, submitted to EPJ
Photon induced Lambda(1520) production and the role of the K^* exchange
We study the photon induced Lambda(1520) production in the effective
Lagrangian method near threshold, E_\gamma^{LAB}<2 GeV, and in the quark-gluon
string model at higher energies 3 GeV < E_\gamma^{LAB} < 5 GeV. In particular,
we study the role of the K^* exchange for the production of Lambda(1520) within
the SU(6) Weinberg-Tomozowa chiral unitary model proposed in Phys. Rev. D74
(2006) 034025. The coupling of the Lambda(1520) resonance to the N \bar K^*
pair, which is dynamically generated, turns out to be relatively small and,
thus, the K exchange mechanism dominates the reaction. In the higher energy
region, where experimental data are available, the quark-gluon string mechanism
with the K Regge trajectory reproduces both the energy and the angular
distribution dependences of the Lambda(1520) photo-production reaction.Comment: 20 pages and 6 page
Aromatic circular dichroism in globular proteins: applications to protein structure and folding
1994 Fall.Includes bibliographical references (pages 334-342).Covers not scanned.Print version deaccessioned 2020.The exciton couplet approach was applied to estimate the circular dichroism (CD) of Trp side-chains in proteins. Calculations were performed by the origin-independent version of the matrix method, either for the indole Bb transition only or for the six lowest energy indole transitions. The dependence of the CD of a Trp pair upon its distance and geometry has been analyzed. It was predicted that mixing with far-uv transitions are as important in determining the CD intensity of the near-uv transitions as the coupling among near-uv transition. The effects of varying exposure of Trp chromophores and nearby charges on Trp CD have been examined. A survey of a large number of proteins from the Protein Data Bank reveals a number of cases where readily detectable exciton couplets are predicted to result from the exciton coupling of Trp Bb bands. The predicted CD spectra are generally couplets, often dominated by the contributions of the closest pair, but sometimes exhibit three distinct maxima. This CD depends on the distance and relative orientation of Trp pairs and thus reflects the spatial arrangement of Trp residues in the protein. It was shown that Trp side chains can make significant contributions to the CD of proteins in the far ultraviolet. The distance dependence of exciton splitting, rotational and couplet strengths of Trp pairs show general agreement with theoretical predictions. In several cases, changes in protein Trp CD can be attributed to a specific Trp pair and explained as a definite change in its conformation. Applications of the exciton couplet approach are discussed for various crystal forms of hen lysozyme, turkey and human lysozyme. Trp62 in hen and turkey lysozymes was found to be sensitive to the perturbations of the protein surface due to binding of substrate, antibodies and intermolecular contacts in the crystal. Conformational changes of Trp62 are predicted to have a strong effect on the overall Trp CD of lysozyme. Predicted Trp CD is compared with experimental results for various lysozymes, a-chymotrypsin and chymotrypsinogen A, concanavalin, dihydrofolate reductase and ribonuclease from Bacillus intermedius 7P (binase). The calculated near-uv CD for hen lysozyme matches the experimental amplitude. Correlation of conformational changes in proteins with Trp CD is shown for a-chymotrypsin and chymotrypsinogen A. We found that the exciton couplet approach might be useful in relating Trp CD and changes in protein structure upon local mutations and conformational changes involved in enzyme activation. Small globular proteins are usually composed of a single structural domain and undergo cooperative denaturation. We have demonstrated that a protein with a single structural domain, binase, and a protein with multiple structural domains, porcine pepsin, contain fewer cooperative regions (energetic domains) under the conditions optimal for their functional activity. The study was performed by combining a CD analysis of the structural changes in the proteins during thermal denaturation and under various solvent conditions with thermodynamic properties observed by scanning microcalorimetry. Estimates of secondary structure were obtained from CD spectra, taking side-chain CD into account. It was found that neither of the proteins show any changes in secondary structure or local environment of aromatic amino acids upon separation of the energetic domains. The structural regions in binase corresponding to energetic domains were identified. It was shown that binase is converted from a single cooperative system into two separate energetic domains when ion pairs are disrupted, whereas the size of cooperative units in pepsin decrease as the electrostatic repulsion between regions in the molecule increases
Polarization observables in high-energy deuteron photodisintegration within the Quark-Gluon Strings Model
Deuteron two-body photodisintegration is analysed within the framework of the
Quark-Gluon Strings Model. The model describes fairly well the recent
experimental data from TJNAF in the few GeV region. Angular distributions at
different -energies are presented and the effect of a forward-backward
asymmetry is discussed. New results from the QGSM for polarization observables
from 1.5 -- 6 GeV are presented and compared with the available data.Comment: 3 pages, LaTeX, 4 postscript figures; contribution to QNP2002,
Juelich, June 10-14, 200
a0(980)-f0(980) mixing and isospin violation in the reactions pN -> d a0, pd -> 3He/3H a0 and dd -> 4He a0
It is demonstrated that f_0-a_0 mixing can lead to a comparatively large
isospin violation in the reactions pN -> da_0, pd -> ^3He/^3H a_0 and dd ->
^4He a_0 close to the corresponding production thresholds. The observation of
such mixing effects is possible, e.g., by measuring the forward-backward
asymmetry in the reaction pn -> d a_0^0 -> d eta pi^0.Comment: 14 pages, 5 figure
Production of -mesons in the reactions and at GeV energies
We investigate the reactions and near
threshold and at medium energies. An effective Lagragian approach and the Regge
pole model are applied to analyze different contributions to the cross section
of the reaction . These results are used to calculate the
differential and total cross sections of the reaction within
the framework of the two-step model in which two nucleons produce an
-meson via -meson exchange and fuse to a deuteron. The necessity of
new measurements on production and branching fractions (of its decay to
the and channels) is emphasized for clarifying the
structure. Detailed predictions for the reaction are presented
for the energy regime of the proton synchrotron COSY-J\"ulich.Comment: 9 pages, including 6 eps figure
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