Shear viscosity, instability and the upper bound of the Gauss-Bonnet coupling constant

We compute the dimensionality dependence of $\eta/s$ for charged black branes with Gauss-Bonnet correction. We find that both causality and stability constrain the value of Gauss-Bonnet coupling constant to be bounded by 1/4 in the infinite dimensionality limit. We further show that higher dimensionality stabilize the gravitational perturbation. The stabilization of the perturbation in higher dimensional space-time is a straightforward consequence of the Gauss-Bonnet coupling constant bound.Comment: 16 pages,3 figures+3 tables,typos corrected, published versio

Rhein induces apoptosis of HCT-116 human colon cancer cells via activation of the intrinsic apoptotic pathway

Rhein, a major compound in rhubarb, has been found to have anti-tumor properties in many human cancer cells. However, the details about rhein suppressing the growth of human colon cancer cells remained elusive. In this paper, we explored the potential of rhein as a chemotherapeutic agent on HCT- 116 cells and demonstrated significant inhibition of HCT-116 cells proliferation in both concentration (0, 10, 30, and 100 μM) and time (24, 48, and 72 h) dependent manners. The anti-tumor effects were associated with the introduction of cellular apoptosis, which was relative with reduction of Bcl-2, NF-κB and activation of caspase-9 and 3. In conclusion, these findings suggested that rhein inhibited the growth of HCT-116 through the intrinsic apoptotic pathway and might be a useful strategy of chemotherapeutics of colon cancers.Key words: Rhein, apoptosis, HCT-116 human colon cancer cells, anti-tumor properties, caspases, Bcl-2 family proteins, NF-κB

Modelling of plate heat exchangers and their associated CO2 trancritical power generation system

Globally, there is no shortage of low-grade waste and renewable heat sources that can be converted into electricity and useful heat using applicable thermodynamic power cycles and appropriate working fluids. As a natural working fluid, CO2 is a promising candidate for application in low-grade power generation systems but require optimised design and evaluation. Since CO2 working fluid has a low critical temperature (31.1⁰C) and high critical pressure (73.8 bar), a CO2 low-grade power generation system will most likely undergo supercritical Rankine (T-CO2) cycles. A T-CO2 system normally consists of a CO2 supercritical gas heater, expander, recuperator, condenser and liquid pump with the CO2 gas heater being a crucial component in determining system thermal and exergy efficiencies. In this paper, the models of a thermal oil-CO2 plate gas heater has been developed and validated with measurements of a 5kWe T-CO2 system test rig. The model is then integrated with other system component models to establish the system model. The system model can be used to evaluate and compare system performances at different operating conditions, including variable CO2 gas heater pressures and heat sink parameters, thereby optimising system operations.The authors would like to acknowledge the support received from GEA Searle and Research Councils UK (RCUK) for this research project

Laser-induced charging of microfabricated ion traps

Electrical charging of metal surfaces due to photoelectric generation of carriers is of concern in trapped ion quantum computation systems, due to the high sensitivity of the ions' motional quantum states to deformation of the trapping potential. The charging induced by typical laser frequencies involved in doppler cooling and quantum control is studied here, with microfabricated surface electrode traps made of aluminum, copper, and gold, operated at 6 K with a single Sr$^+$ ion trapped 100 $\mu$m above the trap surface. The lasers used are at 370, 405, 460, and 674 nm, and the typical photon flux at the trap is 10$^{14}$ photons/cm$^2$/sec. Charging is detected by monitoring the ion's micromotion signal, which is related to the number of charges created on the trap. A wavelength and material dependence of the charging behavior is observed: lasers at lower wavelengths cause more charging, and aluminum exhibits more charging than copper or gold. We describe the charging dynamic based on a rate equation approach.Comment: 8 pages, 8 figure

Reverse Software Engineering

The goal of Reverse Software Engineering is the reuse of old outdated programs in developing new systems which have an enhanced functionality and employ modern programming languages and new computer architectures. Mere transliteration of programs from the source language to the object language does not support enhancing the functionality and the use of newer computer architectures. The main concept in this report is to generate a specification of the source programs in an intermediate nonprocedural, mathematically oriented language. This specification is purely descriptive and independent of the notion of the computer. It may serve as the medium for manually improving reliability and expanding functionally. The modified specification can be translated automatically into optimized object programs in the desired new language and for the new platforms. This report juxtaposes and correlates two classes of computer programming languages: procedural vs. nonprocedural. The nonprocedural languages are also called rule based, equational, functional or assertive. Non-procedural languages are noted for the absence of side effects and the freeing of a user from thinking like a computer when composing or studying a procedural language program. Nonprocedural languages are therefore advantageous for software development and maintenance. Non procedural languages use mathematical semantics and therefore are more suitable for analysis of the correctness and for improving the reliability of software. The difference in semantics between the two classes of languages centers on the meaning of variables. In a procedural language a variable may be assigned multiple values, while in a nonprocedural language a variable may assume one and only one value. The latter is the same convention as used in mathematics. The translation algorithm presented in this report consists of renaming variables and expanding the logic and control in the procedural program until each variable is assigned one and only one value. The translation into equations can then be performed directly. The source program and object specification are equivalent in that there is a one to one equality of values of respective variables. The specification that results from these transformations is then further simplified to make it easy to learn and understand it when performing maintenance. The presentation of translation algorithms in this report utilizes FORTRAN as the source language and MODEL as the object language. MODEL is an equational language, where rules are expressed as algebraic equations. MODEL has an effective translation into the object procedural languages PL/1, C and Ada

Optimal Control of the Stretching Process of Solar Arrays on a Spacecraft Using a Genetic Algorithm

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