Exact solution of the Schrodinger equation with the spin-boson Hamiltonian

We address the problem of obtaining the exact reduced dynamics of the spin-half (qubit) immersed within the bosonic bath (enviroment). An exact solution of the Schrodinger equation with the paradigmatic spin-boson Hamiltonian is obtained. We believe that this result is a major step ahead and may ultimately contribute to the complete resolution of the problem in question. We also construct the constant of motion for the spin-boson system. In contrast to the standard techniques available within the framework of the open quantum systems theory, our analysis is based on the theory of block operator matrices.Comment: 9 pages, LaTeX, to appear in Journal of Physics A: Mathematical and Theoretica

DESIGN OF COOLING SYSTEM FOR PHOTOVOLTAIC PANEL FOR INCREASING ITS ELECTRICAL EFFICIENCY

Photovoltaic solar cell generates electricity by receiving solar irradiance. The temperature of photovoltaic modules increases when it absorbs solar radiation, causing a decrease in efficiency. This undesirable effect can be partially avoided by applying a heat recovery unit with fluid circulation with the photovoltaic module. Such unit is called photovoltaic/thermal collector (PV/T) or hybrid (PV/T). The objective of the present work is to design a system for cooling the solar cell in order to increase its electrical efficiency and also to extract the heat energy. A hybrid solar system which generates both electricity and heat energy simultaneously is studied. This hybrid system consists of PV cells attached to an absorber plate with fins attached at the other side of the absorber surface. Simulation model for single pass, single duct solar collector with fins is prepared and performance curves are obtained. Performance with seven different gases analysed for maximum heat transfer, minimum mass flow rate & minimum number of fins. Hydrogen is found to be the most suitable option with the present. For hydrogen, the system requires a mass flow rate of 0.00275 kg/s, which is the least amongst all. Theoretical number of fins required in this case is found out to be 3.46

52 Realizacja techniki wielkopolowej w napromienianiu ziarnicy złośliwej przy wykorzystaniu systemu przestrzennego planowania teleradioterapii

W roku 1887 w Centrum Onkologii W Warszawie do rutynowego użycia wprowadzono system przestrzennego planowania teleradioterapi TMS-Helax. Umożliwiło to poprawienie jakości planowania w techtechnice wielkopolowej, a zarazem spowodowało szereg zmian w sposobie realizacji tej techniki.Przy leczeniu chłoniaków stosowana jest obecnie wiązka fotonów o energii 6 MeV, która w porównaniu ze stosowaną dotychczas wiązką kobaltową gwarantuje bardziej jednorodny rozkład dawki. Planowanie leczenia odbywa się każdorazowo w oparciu o badanie CT, przy czym skany wykonywane są w całym pasie leczenia z gęstością jeden skan na 1–2 cm. Niemal we wszystkich przypadkach stosowana jest technika izocentryczna. Napromienianie obu pól: przedniego i tylnego odbywa się bez zmiany pozycji ciała pacjenta. Wszyscy pacjenci mają przygotowane osłony indywidualne (ochrona płuc, krtani, nerek). Ich położenie jest weryfikowane poprzez wykonanie zdjęć sprawdzających na akceleratorze. W trakcie radioterapii stosowany jest woskowy bolus umieszczony pod szyją pacjenta, który ma podwójne zadanie: stabilizuje pozycję ciała oraz spełnia rolę kompensatora, dzięki któremu dawka w obszarze szyi jest bliska dawce w punkcie referencyjnym (pkt referencyjny znajduje się w połowie AP, na osi wiązek).W przypadku konieczności łączenia pól odstęp dzymiędzy polami dobierany jest indywidualnie poprzez analizę rozkładu dawki w przekroju strzałkowym

Low dose cranial irradiation-induced cerebrovascular damage is reversible in mice

BACKGROUND: High-dose radiation-induced blood-brain barrier breakdown contributes to acute radiation toxicity syndrome and delayed brain injury, but there are few data on the effects of low dose cranial irradiation. Our goal was to measure blood-brain barrier changes after low (0.1 Gy), moderate (2 Gy) and high (10 Gy) dose irradiation under in vivo and in vitro conditions. METHODOLOGY: Cranial irradiation was performed on 10-day-old and 10-week-old mice. Blood-brain barrier permeability for Evans blue, body weight and number of peripheral mononuclear and circulating endothelial progenitor cells were evaluated 1, 4 and 26 weeks postirradiation. Barrier properties of primary mouse brain endothelial cells co-cultured with glial cells were determined by measurement of resistance and permeability for marker molecules and staining for interendothelial junctions. Endothelial senescence was determined by senescence associated β-galactosidase staining. PRINCIPLE FINDINGS: Extravasation of Evans blue increased in cerebrum and cerebellum in adult mice 1 week and in infant mice 4 weeks postirradiation at all treatment doses. Head irradiation with 10 Gy decreased body weight. The number of circulating endothelial progenitor cells in blood was decreased 1 day after irradiation with 0.1 and 2 Gy. Increase in the permeability of cultured brain endothelial monolayers for fluorescein and albumin was time- and radiation dose dependent and accompanied by changes in junctional immunostaining for claudin-5, ZO-1 and β-catenin. The number of cultured brain endothelial and glial cells decreased from third day of postirradiation and senescence in endothelial cells increased at 2 and 10 Gy. CONCLUSION: Not only high but low and moderate doses of cranial irradiation increase permeability of cerebral vessels in mice, but this effect is reversible by 6 months. In-vitro experiments suggest that irradiation changes junctional morphology, decreases cell number and causes senescence in brain endothelial cells

Energetic instability of passive states in thermodynamics

Passivity is a fundamental concept in thermodynamics that demands a quantum system’s energy cannot be lowered by any reversible, unitary process acting on the system. In the limit of many such systems, passivity leads in turn to the concept of complete passivity, thermal states and the emergence of a thermodynamic temperature. Here we only consider a single system and show that every passive state except the thermal state is unstable under a weaker form of reversibility. Indeed, we show that given a single copy of any athermal quantum state, an optimal amount of energy can be extracted from it when we utilise a machine that operates in a reversible cycle. This means that for individual systems, the only form of passivity that is stable under general reversible processes is complete passivity, and thus provides a physically motivated identification of thermal states when we are not operating in the thermodynamic limit