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Search Results: 1 - 10 of 5453 matches for " Claus Jacob "
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Analysis and Synthesis. Interdependent Operations in Chemical Language and Practice
Claus Jacob
Hyle : International Journal for Philosophy of Chemistry , 2001,
Abstract: Chemical symbolism provides the linguistic representations for experimental research. It is based on an empirical set of formal (syntactic) rules that allows operations on formulas and reaction equations. The semantic interpretation of formulas and reaction equations links these operations to experimental analysis and synthesis. These syntactic and semantic aspects of chemical symbolism guide as well as limit chemical research. A better understanding of these aspects of chemical language allows chemists to rationalize novel approaches to chemical research (e.g. combinatorial chemistry) and possibly exploit the vast area of 'surprise discoveries'.
Teaching Philosophy of Chemistry at the University of Exeter (report)
Claus Jacob,Glenn Jones
Hyle : International Journal for Philosophy of Chemistry , 2003,
Abstract: report of Teaching Philosophy of Chemistry at the University of Exeter
Risk and Responsibility in Chemical Research: The Case of Agent Orange
Claus Jacob,Adam Walters
Hyle : International Journal for Philosophy of Chemistry , 2005,
Abstract: The synthesis of new chemical substances causes a number of ethical problems frequently overlooked by chemists, such as the risk associated with the creation of a new substance and the question of ultimate responsibility for a new compound. The case of the synthesis and subsequent use of Agent Orange can be used to exemplify these issues. Risk as well as responsibility for the agent have shifted significantly since its discovery, from the original inventor of a new compound, via the industrial manufacturer of a dioxin-contaminated herbicide, to the user of the impure agent as tactical chemical weapon in Vietnam. Analyzing the chain of historical events in the light of moral responsibility allows us to set everyday chemistry into an ethical context and ask a number of important questions, such as who carries responsibility for a new chemical compound, its safety and its proliferation.
Potential of the Dietary Antioxidants Resveratrol and Curcumin in Prevention and Treatment of Hematologic Malignancies
Mareike Kelkel,Claus Jacob,Mario Dicato,Marc Diederich
Molecules , 2010, DOI: 10.3390/molecules15107035
Abstract: Despite considerable improvements in the tolerance and efficacy of novel chemotherapeutic agents, the mortality of hematological malignancies is still high due to therapy relapse, which is associated with bad prognosis. Dietary polyphenolic compounds are of growing interest as an alternative approach, especially in cancer treatment, as they have been proven to be safe and display strong antioxidant properties. Here, we provide evidence that both resveratrol and curcumin possess huge potential for application as both chemopreventive agents and anticancer drugs and might represent promising candidates for future treatment of leukemia. Both polyphenols are currently being tested in clinical trials. We describe the underlying mechanisms, but also focus on possible limitations and how they might be overcome in future clinical use – either by chemically synthesized derivatives or special formulations that improve bioavailability and pharmacokinetics.
1,4-Naphthoquinones: From Oxidative Damage to Cellular and Inter-Cellular Signaling
Lars-Oliver Klotz,Xiaoqing Hou,Claus Jacob
Molecules , 2014, DOI: 10.3390/molecules190914902
Abstract: Naphthoquinones may cause oxidative stress in exposed cells and, therefore, affect redox signaling. Here, contributions of redox cycling and alkylating properties of quinones (both natural and synthetic, such as plumbagin, juglone, lawsone, menadione, methoxy-naphthoquinones, and others) to cellular and inter-cellular signaling processes are discussed: (i) naphthoquinone-induced Nrf2-dependent modulation of gene expression and its potentially beneficial outcome; (ii) the modulation of receptor tyrosine kinases, such as the epidermal growth factor receptor by naphthoquinones, resulting in altered gap junctional intercellular communication. Generation of reactive oxygen species and modulation of redox signaling are properties of naphthoquinones that render them interesting leads for the development of novel compounds of potential use in various therapeutic settings.
Simultaneous Echo Refocused Magnetization Transfer Imaging  [PDF]
Claus Kiefer
Open Journal of Medical Imaging (OJMI) , 2014, DOI: 10.4236/ojmi.2014.43021
Abstract: Purpose: To increase the efficiency of densely encoded magnetization transfer imaging of the brain, we time-multiplex multiple slices within the same readout using simultaneous echo refocusing FLASH imaging with magnetization transfer (MT) preparation (MT-SER-FLASH). Materials and Methods: Inefficiency in total scan time results from the number of frequency samples needed for sufficient quality of quantitative parameter maps for a binary spin bath model. We present a highly efficient multiplexing method, simultaneous echo refocused magnetization transfer imaging (MT-SER-FLASH) for reducing the total scan time of MT imaging by one-third. The specific absorption rate (SAR) was also reduced by reducing the number of MT-pulses per volume. Results: 2D-MT-SER-FLASH is performed in 19 minutes rather than 1 hour, acceptable for routine clinical application. The SAR could be reduced to 69% instead of more than 100% with a standard 2D or 3D-FLASH with MT-preparation. Conclusion: The net reduction of scan time and SAR enables the use of quantitative model based magnetization transfer imaging within a clinical environment.
Modelling Magnetization Transfer Considering Spin-Locking Effects  [PDF]
Claus Kiefer
Open Journal of Medical Imaging (OJMI) , 2014, DOI: 10.4236/ojmi.2014.44027
Abstract: Purpose: Recently it was demonstrated that spin-locking (SL) effects can manifest as pseudo magnetization transfer (MT). To our best knowledge the MT models proposed so far cannot distinguish between saturation effects caused by the MT preparation pulses and SL phenomena. Therefore a new MT model is proposed. Materials and Methods: A binary spin-bath model for magnetization transfer was extended in that sense that SL effects are considered. The new modified spin bath model was tested for a phantom with different agar concentrates (2%, 4%, 8%) and a MnCl2 (0.3 mM) solution. Results: The mean fitting error is 3.2 times lower for the modified model compared to the original model. Especially the parameter F for the fractional part of the bounded proton pool describes the situation for the MnCl2 (F = 0) better than the original model (F = 0.004). Conclusion: The proposed mathematical modifications of the binary spin-bath model considering SL seem to be a step in the right direction in that sense that the effects associated with SL are not interpreted as magnetization transfer.
Male dominance linked to size and age, but not to 'good genes' in brown trout (Salmo trutta)
Alain Jacob, Sébastien Nusslé, Adrian Britschgi, Guillaume Evanno, Rudolf Müller, Claus Wedekind
BMC Evolutionary Biology , 2007, DOI: 10.1186/1471-2148-7-207
Abstract: We found significant additive genetic variance on embryo survival, i.e. males differed in their genetic quality. Older, heavier and larger males were more successful in intra-sexual selection. However, neither dominance nor dominance indicators like body length, weight or age were significantly linked to genetic quality measured as embryo or juvenile survival.We found no evidence that females can improve their offspring's genetic viability by mating with large and dominant males. If there still were advantages of mating with dominant males, they may be linked to non-genetic benefits or to genetic advantages that are context dependent and therefore possibly not revealed under our experimental conditions – even if we found significant additive genetic variation for embryo viability under such conditions.In mating systems with elaborate male-male competition, the winners usually get most mates and sire most of the offspring [1-10]. Such a skewed male mating success may either be explained by physically limited access of subdominant males to females and/or by female preference for dominant males [11-13]. Females may prefer more dominant and more attractive males because they provide more resources, better parental care [14,15] or better genes for the common offspring [2,16-18]. The latter hypothesis corresponds to the so-called 'good-genes' hypotheses of sexual selection, i.e. variation in genetic quality is then predicted to be linked to male characteristics that influence female mate choice. The problem of how such genetic variation can be maintained under sexual selection is known as the "lek paradox" [19], and a number of possible solutions for this paradox have been offered (reviewed in [20,21]). Although it is still not fully clear how the genetic variation is maintained, there is much evidence in various species that females can gain genetic advantages by preferring males with well-developed attractiveness traits [22]. Whether females gain genetic benefits by mat
Many Roads to Paris: A Comparative Review of Pension Policies in Two OECD Countries  [PDF]
Jacob Assa
Modern Economy (ME) , 2011, DOI: 10.4236/me.2011.25095
Abstract: Common (neoliberal) wisdom warns against the detrimental effects of demographic changes and fiscal pressures on traditional (both defined-benefit and public) pensions and urges a paradigm shift towards defined- contribution plans and personal retirement accounts. This paper examines these claims, promoted by the OECD and World Bank, among others, by comparing the experiences of two OECD members—Israel and Ireland. While Ireland, one of the founders of the OECD, has pursued typical neoliberal policies of retrenchment, Israel—the newest member of the OECD—has taken a more sinuous path, reversing some retrenchment and eventually making pensions mandatory and almost doubling employer contributions to them. The outcomes of these policies seem to be far more positive in Israel than in Ireland, both in terms of their effects on retirees and workers, as well as their impact via aggregate demand on the overall economy, particularly in the aftermath of the Great Recession.
Inequality and Growth Re-Examined  [PDF]
Jacob Assa
Technology and Investment (TI) , 2012, DOI: 10.4236/ti.2012.31001
Abstract: This paper examines the relationship between income inequality and subsequent economic growth. It builds on the model suggested by Alesina and Rodrik (1994) in which inequality works through greater demands for redistribution to slow down growth, and the idea by Ray (1998) that inequality negatively affects savings, work capacity, economic incentives, and access to and efficiency of credit and financial markets. Using an updated dataset and seven model variants, both OLS and 2SLS regressions find a strong negative effect of income inequality on future growth. The effect is considerably stronger for developing countries, but the existence or absence of democracy has no effect on either the relationship between inequality and growth or on the rate of growth itself. There is also no support for Barro’s (2008) claim that inequality impacts growth positively in developed countries.
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