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Search Results: 1 - 10 of 167834 matches for " E. Mach "
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Geometry of Keplerian disk systems and bounds on masses of their components
E. Malec,P. Mach,M. Pirog
Physics , 2012,
Abstract: We investigate accreting disk systems with polytropic gas in Keplerian motion. Numerical data and partial analytic results show that the self-gravitation of the disk speeds up its rotation -- its rotational frequency is larger than that given by the well known strictly Keplerian formula that takes into account the central mass only. Thus determination of central mass in systems with massive disks requires great care -- the strictly Keplerian formula yields only an upper bound. The effect of self-gravity depends on geometric aspects of disk configurations. Disk systems with a small (circa $10^{-4}$) ratio of the innermost radius to the outermost disk radius have the central mass close to the upper limit, but if this ratio is of the order of unity then the central mass can be smaller by many orders of magnitude from this bound.
Synthesis of an antiviral drug precursor from chitin using a saprophyte as a whole-cell catalyst
Matthias G Steiger, Astrid R Mach-Aigner, Rita Gorsche, Erwin E Rosenberg, Marko D Mihovilovic, Robert L Mach
Microbial Cell Factories , 2011, DOI: 10.1186/1475-2859-10-102
Abstract: In this study, we introduced two enzymes from bacterial origin into Hypocrea, which convert GlcNAc into NeuNAc via N-acetylmannosamine. This enabled the fungus to produce NeuNAc from the cheap starting material chitin in liquid culture. Furthermore, we expressed the two recombinant enzymes as GST-fusion proteins and developed an enzyme assay for monitoring their enzymatic functionality. Finally, we demonstrated that Hypocrea does not metabolize NeuNAc and that no NeuNAc-uptake by the fungus occurs, which are important prerequisites for a potential production strategy.This study is a proof of concept for the possibility to engineer in a filamentous fungus a bacterial enzyme cascade, which is fully functional. Furthermore, it provides the basis for the development of a process for NeuNAc production as well as a general prospective design for production processes that use saprophytes as whole-cell catalysts.NeuNAc is the most prevalent exponent of sialic acids [1]. In mammals, sialic acids are usually found as terminal residues of glycol conjugates on the outermost cell surface. As a result of their location and their negative carboxylate functionality, sialic acids play important roles in mediating cellular recognition and adhesion processes [2] and in the infection cycles of severe viral diseases, such as influenza viruses A and B [3]. In these cases, de novo-synthesized viral particles attach to their respective sialic acids at the cell surface. Neuraminidase (sialidase) activity is needed for the propagation of the virus in the host. Consequently, sialic acid derivatives are successfully applied in the therapy of such virus-related diseases. One well-known product that functions as a neuraminidase inhibitor is Relenza. Its active pharmaceutical ingredient is Zanamivir, which is a direct derivative of the NeuNAc precursor [4].Traditionally, NeuNAc is prepared through extraction from natural sources, such as bird nests, milk, or eggs [5], through the hydrolysis of co
Prostaglandyny a przewód pokarmowy
Tomasz Mach
Pediatria Wspó?czesna , 2004,
Abstract: Prostaglandyny (PG) s wydzielane przy udziale cyklooksygenaz (COX) COX-1, COX-2 i COX-3. COX-1 jest enzymem konstytutywnym, odpowiada za cytoprotekcj , kr enie nerkowe, agregacj p ytek krwi. Objawy uboczne po niesteroidowych lekach przeciwzapalnych (NSAID - nonsteroidal anti-inflamma-torydrugs) - owrzodzenia, krwawienia, zaburzenia hemostazy - s wynikiem hamowania COX-1. COX-2 jest indukowana przez czynniki prozapalne i karcynogenne. Zwi kszon ekspresj COX-2 stwierdzono w wielu nowotworach gruczo owych przewodu pokarmowego. Selektywne inhibitory COX-2 próbuje si wykorzysta w chemoprewencji raka jelita grubego i w zapobieganiu polipom. Analogi PGE wykazuj wp yw na przewód pokarmowy, hamuj c wydzielanie o dkowe i wzmagaj c mechanizmy ochronne b ony luzowej, co zosta o wykorzystane w terapii gastropatii po NSAID. Ostatnio zwraca si uwag na reguluj c rol PG w centralnym systemie nerwowym na czynno przewodu pokarmowego.
Stosowanie leków przeciwwrzodowych u kobiet w ci y
Tomasz Mach
Polish Gastroenterology , 1998,
Abstract: Przedstawiono wspó czesne pogl dy na stosowanie leków przeciwwrzodowych u kobiet w ci y i w okresie laktacji. W czasie ci y wszystkie leki powinny by stosowane z du ostro no ci i tylko gdy istniej bezwzgl dne wskazania, w minimalnych skutecznych dawkach i przez jak najkrótszy okres. Najniebezpieczniejszym okresem szkodliwego dla p odu dzia ania leku podawanego ci arnej kobiecie jest pierwszy trymestr ci y, w którym dokonuje si organogeneza. Podawanie leku kobiecie w ci y w drugim i trzecim trymestrze jest równie niebezpieczne, chocia w mniejszym stopniu. Zwrócono uwag , e poza prowadzeniem badań do wiadczalnych nie wykonuje si badań klinicznych u kobiet w ci y i st d producenci leków z regu y nie zezwalaj na ich przyjmowanie w tym okresie. Omówiono krótko poszczególne grupy leków stosowanych w chorobie wrzodowej, uwzgl dniaj c ich wp yw na transport o yskowy, p ód i przebieg porodu. Przedstawiono stosowane w wielu krajach klasyfikacje leków podawanych kobiecie w ci y i w okresie karmienia, które opracowano na podstawie ich wch aniania, dzia ania ogólnego i powodowania wad wrodzonych. Wielu autorów publikowanych prac uwa a, e s abo wch aniane alkalia i sukralfat oraz blokery receptorów H2 s podstawowymi lekami przeciwwrzodowymi, które mo na podawa ci arnym kobietom, zachowuj c wszelkie zasady ostro no ci. Wzgl dnie bezpieczne podczas ci y, szczególnie w drugim i trzecim trymestrze, jest podawanie leków hamuj cych wydzielanie kwasu solnego, a zw aszcza H2 blokerów, które mog by stosowane w ci szych przypadkach, gdy korzy ci terapii przewy szaj ewentualne ryzyko wyst pienia polekowych objawów ubocznych.
On the stability of steady general-relativistic accretion and analogue black holes
Patryk Mach
Physics , 2009, DOI: 10.1016/S0034-4877(09)90031-3
Abstract: Investigation of general-relativistic spherically symmetric steady accretion of self-gravitating perfect fluid onto compact objects reveals the existence of two weakly accreting regimes. In the first (corresponding to the test fluid approximation) the mass of the central object is much larger than the mass of the accreting fluid; in the second the mass of the fluid dominates. The stability of the solutions belonging to the first regime has been proved by Moncrief. In this work we report the results of a series of numerical studies demonstrating stability of massive solutions, i.e., belonging to the second of the aforementioned regimes. It is also shown that a formal analogy between "sonic horizons" in the accretion picture and event horizons in general relativity is rather limited. The notion of a "sonic horizon" is only valid in a linear regime of small hydrodynamical perturbations. Strong perturbations can still escape from beneath the "sonic horizon."
All solutions of the n = 5 Lane-Emden equation
Patryk Mach
Physics , 2012, DOI: 10.1063/1.4725414
Abstract: All real solutions of the Lane-Emden equation for n = 5 are obtained in terms of Jacobian and Weierstrass elliptic functions. A new family of solutions is found. It is expressed by remarkably simple formulae involving Jacobian elliptic functions only. The general properties and discrete scaling symmetries of these new solutions are discussed. We also comment on their possible applications.
Virial theorem for radiating accretion discs
Patryk Mach
Physics , 2011, DOI: 10.1111/j.1365-2966.2012.20658.x
Abstract: A continuum version of the virial theorem is derived for a radiating self-gravitating accretion disc around a compact object. The central object is point-like, but we can avoid the regularization of its gravitational potential. This is achieved by applying a modified Pohozaev-Rellich identity to the gravitational potential of the disk only. The theorem holds for general stationary configurations, including discontinuous flows (shock waves, contact discontinuities). It is used to test numerical solutions of a model of self-gravitating radiative accretion discs. The presented virial theorem should be useful in the analysis of those (possibly radiating) hydrodynamical systems in astrophysics where the central mass and the mass of the fluid are comparable and none of them can be neglected.
Analytic solutions of the Riemann problem in relativistic hydrodynamics and their numerical applications
Patryk Mach
Physics , 2010,
Abstract: We present an analytic solution of the Riemann problem for the equations of relativistic hydrodynamics with the ultra-relativistic equation of state and non-zero tangential velocities. A 3-dimensional numerical code solving such equations is described and then tested against the analytic solution.
Corrugation instabilities of the Riemann problem in relativistic hydrodynamics
Patryk Mach
Physics , 2011, DOI: 10.1063/1.4734459
Abstract: Corrugation instabilities occurring for solutions of the Riemann problem in relativistic hydrodynamics in which the fluid moves with a non-zero velocity tangent to the initial discontinuity are studied numerically. We perform simulations both for ultrarelativistic and perfect gas equations of state. We focus on a set of problems with moderately relativistic velocities but exhausting all possible wave patterns of solutions. Perturbations are applied to the shape of the initial discontinuity. Instabilities that develop are only restricted to a region around a contact discontinuity. Both shock and rarefaction waves appear to be stable.
恢复人体四肢活动功能的肌电机器人技术系统
Mach.,RS
重庆大学学报 , 1989,
Abstract: 本文提出了一种适用于恢复人体四肢活动的机器人技术系统。文中指出:应用可按受肌肉功能状态信号的肌电系统,校正机器人执行机构运动参数,原则上是完全可行的。以人体前肢的活动训练为例,给出了由两个二自由度机器人构成的机器人技术系统的仿真研究结果。
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