Irreversible Type Research Articles

Continuous and reversible operation of Bi2212 based THz emitters just below [formula omitted

Continuous and reversible operation of the THz-light emitters comprised of the intrinsic Josephson junction (iJJ) system of high-Tc superconductor Bi2Sr2CaCu2O8+δ (Bi2212) is reported. This reversible emission is observed in samples made of lightly underdoped crystals when a part of the mesa device is so overheated by Joule heating that the temperature reaches Tm near but still below Tc, while the irreversible type of emission occurs at less overheated condition. The large temperature gradient in the mesa due to overheating under high bias currents seems to be responsible for the new observed reversible emission.

The effect of an external magnetic field on the entropy generation in three-dimensional natural convection

A 3-D original numerical study of entropy generation in the case of liquid metal laminar natural convection in a differentially heated cubic cavity and in the presence of an external magnetic field orthogonal to the isothermal walls is carried out. The effect of this field on the various types of irreversibilities is analyzed. It was observed that in the presence of a magnetic field the generated entropy is distributed on the entire cavity and that the magnetic field limits the 3-D character of the distribution of the generated entropy.

Recent Developments of Steroid Sulfatase Inhibitors as Anti-Cancer Agents

The steroid sulfatase (STS) enzyme plays a pivotal role in the formation of biologically active steroid hormones. Its involvement in the hydrolysis of estrone sulfate and dehydroepiandrosterone sulfate to estrone and dehydroepiandrosterone, respectively, is an important step in the formation of estradiol and androstenediol, both of which are estrogenic steroids that can stimulate tumor growth. Consequently, as STS is widely distributed throughout the entire body, it has a substantial influence on hormone-dependent cancer mitogenesis. It is a useful prognostic marker of disease as a significant majority of breast tumors over-express the enzyme and there are indications of STS having a role in prostate cancer. This knowledge has led to the development of potent STS inhibitors for use as anti-cancer agents. There are now several steroidal and non-steroidal STS inhibitors available. New in vivo models, using ovariectomized female nude mice, have been developed to pre-clinically test these inhibitors. These studies have demonstrated the excellent efficacy and effect of STS inhibitors on breast carcinoma development. Recently, 667 COUMATE, an irreversible type of inhibitor which utilizes a phenol sulfamate ester as its active pharmacophore, has completed a Phase I clinical trial in postmenopausal women with breast cancer. These studies have indicated the potential clinical benefit for the use of STS inhibitors. Most pre-clinical and clinical studies have focused on breast cancer as the target for STS inhibition. However, there are other hormone-dependent malignancies, such as endometrial and prostate cancer, that could in the future be treated with these new potent STS inhibitors.

Finite volume computations of convective exergy losses in microfluidic devices

Exergy losses affect the net power required to transport fluid through microfludic devices. Unlike pressure losses or friction factors, modelling of exergy losses can encompass all types of irreversibilities within a microsystem, including thermofluid, chemical and electromagnetic irreversibilities. In this paper, a finite volume method with a SIMPLEC formulation is developed to predict exergy losses in microchannels. The continuum Navier?Stokes equations are solved numerically with a slip-flow boundary condition. The implications of the two coefficients on exergy destruction, involved in the first-order boundary model, are investigated. By reducing exergy destruction within the microchannel, pressure losses and fluid friction can be minimised to reduce power input and improve overall energy efficiency.

An ecological optimisation of an irreversible radiative type heat engine

SYNOPSIS Finite time thermodynamics with an ecological criterion is applied to an irreversible radiative type heat engine with losses due to heat transfer across finite temperature differences and internal irreversibilities. The ecological function, defined as the power output minus the lost power or the product of environmental temperature and the entropy production rate, is optimised with respect to the cycle temperature ratio. The maximum of the ecological function and the corresponding optimal conditions have been derived analytically. The effects of internal irreversibilities and the extreme temperature ratio on the global and optimal performances have been investigated. The obtained results are compared with those obtained by using the maximum power criterion. The results show that the design parameters at the maximum ecological function lead to more efficient heat engines and are a compromise between the power output and the thermal efficiency or entropy generation rate. Moreover, from the viewpoint of the ecological function, the con-duction allocation parameter and extreme temperature ratio should be on the lower side of unity.

Time reversibility of stationary regular finite-state Markov chains

We propose an alternate parameterization of stationary regular finite-state Markov chains, and a decomposition of the parameter into time reversible and time irreversible parts. We demonstrate some useful properties of the decomposition, and propose an index for a certain type of time irreversibility, applicable to chains whose states are naturally ordered. Two empirical examples illustrate the use of the proposed parameter, decomposition and index. One, on gasoline price mark-ups, involves observed states. The other, on U.S. investment growth, features latent states.

Performance comparison of an irreversible closed variable temperature heat reservoir Carnot engine under maximum power density and maximum power conditions

SYNOPSIS In this paper, power density, defined as the ratio of power output to maximum specific volume in the cycle, is taken as the objective for performance analysis and optimisation of an irreversible Carnot heat engine from the viewpoint of finite time thermodynamics. The engine, coupled to variable temperature heat reservoirs, includes three types of irreversibilities: finite rate heat transfer, heat leakage and internal irreversibility. The results obtained here are compared with those obtained by using the maximum power criterion. The design parameters under optimal conditions have been derived analytically and the effects of the irreversibilities on the general and optimal performances are investigated. The results show that the design parameters at maximum power density lead to smaller and more efficient heat engines. It is also seen that the irreversibilities have a greater influence on the performance at maximum power density conditions than that at maximum power conditions. Also in this analysis, the optimum conductance allocation parameter is analysed at both maximum power density and maximum power conditions by assuming a constrained total thermal conductance. The analytical expressions between the conductance allocation parameter and the thermal efficiency are obtained. The obtained results generalise the results of previous studies and provide guidance for optimal design in terms of power, thermal efficiency and engine sizes for real heat engines. When the heat transfers between the working fluid and the heat reservoirs are carried out ideally and the thermal capacity rates of the heat reservoirs are infinite, the results of this paper then replicate those obtained in recent literature.

Practical Management of Dementia: A Multi-Professional Approach

Back to table of contents Previous article Next article Book Forum: Geriatric PsychiatryFull AccessPractical Management of Dementia: A Multi-Professional ApproachPHILIP G. JANICAK, M.D., PHILIP G. JANICAKSearch for more papers by this author, M.D., Chicago, Ill.Published Online:1 May 2005https://doi.org/10.1176/appi.ajp.162.5.1033AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail As the general population (and by inference, each of us) anticipates an increasingly longer lifespan, the problem of dementia also looms larger and may reach epidemic proportions at its present rate of growth. Thus, we anxiously await dividends from an expanding body of work in the fields of genetics, molecular biology, and neuroimaging that may reveal the cause(s) and effective treatment(s) for this condition. In the meantime, a cohesive strategy is required to care for those suffering from serious cognitive decline.In this context, Curran and Wattis have prevailed upon a multidisciplinary group of experts to outline a very readable and comprehensive approach to caring for those with Alzheimer’s dementia and related disorders. Their stated goal is to bridge the gap between the existing knowledge base derived from research in this area and the ability of clinicians to apply this information in a strategy that optimizes patient care. Their stated agenda is to contribute meaningfully to the process of training practitioners to identify dementia as early as possible, respect patient autonomy, and employ treatment approaches that emphasize the spiritual needs of the individual. The discussion from several perspectives results in some repetition, but, overall, the book is a sound review of our present knowledge about the dementias and their management.The editors have divided the text loosely into three parts. The first reviews the history, definition, epidemiology, diagnosis, classification, and strategies for early identification. They note that age is the single most important risk factor. Family history, certain genetic variations (e.g., APOE, E4 homozygotes), and depression are also important predisposing factors that may increase the risk substantially. Conversely, there is preliminary evidence indicating that such disparate factors as regular physical activity; the use of wine, coffee, statins, nonsteroidal antiinflammatory drugs, certain vitamins (e.g., C and E); and higher educational attainment (as well as length of training) may reduce the risk of dementia.The chapter authors underscore that dementia is a syndrome with multiple causes, such as vitamin deficiencies, infections, and endocrine dysfunction—conditions that may be correctible, or at least substantially improved. They highlight the three most common irreversible types (i.e., Alzheimer’s disease, vascular dementia, and Lewy body dementia), noting that accurate and early diagnosis can have a favorable impact on both treatment and prognosis. In this light, they review a number of simple early screening assessments, but they also note that there is no pathognomonic test for Alzheimer’s disease.The second part uses case examples to clarify the role of different professionals (i.e., consultants, psychologists, physicians, nurses, and occupational therapists) in the assessment, diagnosis, and management of dementia. One chapter is devoted to each profession’s unique perspective, emphasizing the need to shift from a medical model orientation to a positive person-centered approach to care.The third part examines the delivery care system for the dementias, focusing on the memory clinic, legal aspects, and the spiritual needs of the individual.The strength of this book is the inclusion of multiple perspectives, but the weakness is substantial redundancy. Despite the latter, I believe that this is an important consolidation of our present knowledge and a good primer for those involved in the care of the dementias.Edited by Stephen Curran and John P. Wattis. Abingdon, Oxon, U.K., Radcliffe Medical Press, 2004, 248 pp., £27.95. FiguresReferencesCited byDetailsCited ByNone Volume 162Issue 5 May 2005Pages 1033-1033 Metrics PDF download History Published online 1 May 2005 Published in print 1 May 2005

Exergy optimization for an irreversible combined cogeneration cycle

Exergy optimization is presented for an irreversible combined cogeneration cycle which includes three types of irreversibilities: finite rate heat transfer, heat leakage and internal irreversibility. The optimal design conditions at maximum exergy output and maximum exergy efficiency output were determined. The effects of the internal irreversibility, heat leakage and heat to power ratio on the exergetic performance are investigated and the results are discussed. It is shown that the optimal exergetic performance intervals stay approximately constant with power to process heat ratio, but they decrease with irreversibility parameter.

Steroid Sulfatase: Molecular Biology, Regulation, and Inhibition

Steroid sulfatase (STS) is responsible for the hydrolysis of aryl and alkyl steroid sulfates and therefore has a pivotal role in regulating the formation of biologically active steroids. The enzyme is widely distributed throughout the body, and its action is implicated in physiological processes and pathological conditions. The crystal structure of the enzyme has been resolved, but relatively little is known about what regulates its expression or activity. Research into the control and inhibition of this enzyme has been stimulated by its important role in supporting the growth of hormone-dependent tumors of the breast and prostate. STS is responsible for the hydrolysis of estrone sulfate and dehydroepiandrosterone sulfate to estrone and dehydroepiandrosterone, respectively, both of which can be converted to steroids with estrogenic properties (i.e., estradiol and androstenediol) that can stimulate tumor growth. STS expression is increased in breast tumors and has prognostic significance. The role of STS in supporting tumor growth prompted the development of potent STS inhibitors. Several steroidal and nonsteroidal STS inhibitors are now available, with the irreversible type of inhibitor having a phenol sulfamate ester as its active pharmacophore. One such inhibitor, 667 COUMATE, has now entered a phase I trial in postmenopausal women with breast cancer. The skin is also an important site of STS activity, and deficiency of this enzyme is associated with X-linked ichthyosis. STS may also be involved in regulating part of the immune response and some aspects of cognitive function. The development of potent STS inhibitors will allow investigation of the role of this enzyme in physiological and pathological processes.

Spin density wave glass in Cr dilute alloys with Fe and Co

The measurements of magnetization M(T) in bulk SDW alloys Cr1-xCox and (Cr+2.7%Fe)1-xCox in ZFC and FC states in magnetic field 100Oe with a SQUID magnetometer have revealed two types of magnetic irreversibility (thermal hysteresis between magnetization measured in FC and ZFC states, MFC(T),MZFC(T)). The first one is observed in alloys with both incommensurate (I) and commensurate (C) SDW structures below the temperature Ti much lower than the Néel temperature, TN. It has been explained in terms of a short range SDW order (“local SDW'') on the defect. The second one is observed below Ti∼TN only for Cr alloys with the I-SDW structure. It has been attributed to the mechanism of the SDW phase slip on the defect inside the “SDW soliton wall''. Depending on the field cooled procedure the alloy Cr+1.19%Co with the I-SDW structure shows the first or the second type of magnetic irreversibility, however, if the C-SDW phase is induced by Fe-doping only the first type of magnetic irreversibility can be observed. The temperature dependence of the remanent magnetization, MRem(T), observed in all studied alloys can be well simulated using the proposed models.

Fabrication and magnetic behaviour of superconductor nanowire arrays

Superconducting Pb nanowire arrays with diameters of about 45 nm have been fabricatedby electrodeposition using anodic porous alumina templates. The Pb nanowires were ofcrystalline face-centre cubic structure and structurally uniform. The temperaturedependence of their magnetic behaviour was investigated. The Pb nanowire arrays exhibitanisotropy, and the Meissner effect of the nanowires is entirely different from that of thebulk Pb; irreversible type II superconductor behaviour has been observed in the Pbnanowires at 5 K.

Spin-density-wave glass state in Cr-based alloys with 3d impurities

Abstract A spin-density-wave (SDW) glass state has been found in Cr alloys. Magnetization measurements in ZFC and FC states have revealed two types of magnetic irreversibility (MI). The first one is caused by a “local SDW”. Depending on the electron concentration of impurity a temperature of divergence of M ZFC ( T ) and M FC ( T ), T i , can be either below or above T N . The second type of MI is due to the deformation of the soliton wall of the SDW domains and can be realized only in Cr alloys with an incommensurate SDW structure just below T N .

Uncertainty and Option Value in Land Allocation Problems

In this paper we are concerned with modelling techniques for evaluating development and conservation opportunities when dealing with investment decisions involving environmental resources management. In this context, highly characterized by both environmental and economic uncertainty, we emphasize the importance of capturing the flexibility of different investment strategies. In particular, we discuss a discrete model that includes both environmental and economic uncertainty treated using an integrated approach. Decision analysis techniques and option pricing theory are jointly applied to evaluate development versus conservation opportunities. In our analysis, we take into account how uncertainty interacts with two types of irreversibility: sunk costs associated with investment in developing decisions, including environmental and social costs, as well as sunk costs associated with environmental regulation and conservation. The Quasi Option Value, QOV, is used to derive decision rules that account for different levels of flexibility of land allocation possibilities.

On the two principal curvatures as potential barriers in a model of complex matter agglomeration

We show that matter agglomeration mesoscopic phenomena of irreversible type are well described by nonequilibrium thermodynamics formalism. The description assumes that the thermodynamic (internal) state variables are in local equilibrium, and uses the well-known flux–force relations, with the Onsager coefficients involved, ending eventually up at a local conservation law of the Fokker–Planck type. Within the framework of the formalism offered the first two curvatures, characterizing the structure of the agglomerates, are associated with a suitable choice of a physical potential governing the system. It turns out that a certain choice of the potential of power-law type leads to emphasizing the role of the Gaussian curvature while another choice in logarithmic form results in a pronounced role of the mean curvature. The offered modeling has been related successfully with a statistical-mechanical polycrystalline matter evolution introduced for physical–metallurgical purposes, and modified for a use in biophysical soft-matter agglomerations. � 2003 Elsevier Science B.V. All rights reserved.

Inorganic ion exchangers in radioactive waste management

The removal behavior of stannic and zirconium phosphates was assessed for Sr(II) ions as a function of sorptive concentration, temperature and pH. It was observed that an increase of these parameters enhanced the removal of Sr(II) ions from aqueous solutions. First order uptake of Sr(II) followed the Freundlich adsorption isotherm for the entire range of sorptive concentration (10-2 to 10-8 mol.dm-3). The study of temperature dependence showed that the endothermic and irreversible type of uptake proceeds by an ion-exchange type mechanism.

Quasi Option Value and Irreversible Choices

In this paper we are concerned with optimal investment decisions when dealing with land allocation problems. We aim to emphasise the importance of flexible modelling in order to capture irreversibility. In particular, we stretch a discrete model, firstly developed in Coggins and Ramezani (Coggins & Ramezzani, 1998), in order to cover a more realistic and complex scenario. Both environmental and economic uncertainty are included in the model and treated using an integrated approach, in which decision analysis techniques and option pricing theory are jointly applied to evaluate development versus conservation opportunities. Moreover, we take explicit account of how uncertainty interacts with two types of irreversibility: sunk costs associated with investment in developing decisions, including environmental and social costs due to environmental degradation, as well as sunk costs associated to environmental regulation and conservation. Finally, we use the Quasi Option Value, to derive decision rules that account for different levels of flexibility of land allocation possibilities.

Serum surfactant proteins A and D as prognostic factors in idiopathic pulmonary fibrosis and their relationship to disease extent.

Idiopathic pulmonary fibrosis (IPF) is a progressive, life-threatening, interstitial lung disease of unknown etiology. For optimal therapeutic management of IPF an accurate tool is required for discrimination between reversible and irreversible types of the disease. However, such noninvasive tools are few, and even with high-resolution computed tomography (HRCT), which is the most trusted method for doing so, the nature of the disease activity in IPF cannot always be accurately predicted. The aims of the present study were to assess the values of surfactant protein (SP)-A and SP-D in semiquantifying the extent of disease in IPF and in predicting deterioration in restrictive pulmonary function and survival over a follow-up period of 3-yr. SP-A and SP-D in sera were measured with enzyme-linked immunosorbent assays as previously described. Fifty-two IPF patients were studied to evaluate the association between serum SP-A and SP-D and disease extent on HRCT, deterioration in pulmonary function, and survival during 3 yr of follow-up. Both SP-A and SP-D concentrations were significantly correlated with the extent of alveolitis (a reversible change), whereas they did not correlate with the progression of fibrosis (an irreversible change). The SP-D concentration, unlike that of SP-A, was also related to the extent of parenchymal collapse and the rate of deterioration per year in pulmonary function. The concentrations of SP-A and SP-D in patients who died within 3 yr were significantly higher than in patients who were still alive after 3 yr. We propose that assays of SP-A and SP-D in sera from IPF patients are useful tools for understanding some pathologic characteristics of the disease, that SP-D may be a good predictive indicator of the rate of decline in pulmonary function, and that a combination of the assays for SP-A and SP-D may be helpful in predicting the outcome of patients with IPF.

Effect of MAO-B inhibitors on MPP+ toxicity in Vivo.

l-Deprenyl (Selegiline), a selective and irreversible type B monoamine oxidase inhibitor, has been used as an adjunct to levodopa therapy in Parkinson's disease. Recently, it is proposed as a putative neuroprotective agent in delaying the progression of cell death based on its capability of reducing the oxidative stress derived from the MAO-B dependent metabolism of dopamine, and blocking the development of MPTP-parkinsonism. However, a variety of experimental models suggest that l-deprenyl provides neuroprotection through multiple modes of mechanism other than the inhibition of MAO-B. We have previously shown that l-deprenyl protects midbrain dopamine neurons from MPP+ toxicity by a novel antioxidant effect. In the present study we examined whether the protection against MPP+ toxicity is also shared by other reversible or irreversible MAO-B inhibitors including (+)-deprenyl, Ro16-6491 and pargyline. Our data show that non of these MAO-B inhibitors changes the dopamine loss in the striatum induced by intranigral injection of MPP+. Our result suggests that l-deprenyl may possess a unique neuroprotective action on nigral neuron against MPP+ toxicity independent of the MAO-B inhibition.

A comparative performance analysis of irreversible Carnot heat engines under maximum power density and maximum power conditions

This paper reports the finite time thermodynamic optimization based on the maximum power density criterion for an irreversible Carnot heat engine model which includes three types of irreversibilities: finite rate heat transfer, heat leakage and internal irreversibility. The obtained results are compared with those results obtained by using the maximum power criterion. The design parameters under the optimal conditions have been derived analytically and the effects of the irreversibilities on the general and optimal performances are investigated. The results showed that the design parameters at maximum power density lead to smaller and more efficient heat engines. It is also seen that the irreversibilities have a greater influence on the performances at maximum power density conditions with respect to the ones at maximum power conditions. Also in this study, the optimal conductance allocation parameter is investigated at both maximum power density and maximum power conditions by assuming a constrained total thermal conductance in the case when there is no heat leakage. The relation between the conductance allocation parameter and the thermal efficiencies at maximum power density and maximum power is also investigated. The obtained results generalize the result of previous studies on this subject and provide guidance to optimal design in terms of power, thermal efficiency and engine sizes for real heat engines.