Osmoregulation of chloride channels in epithelial cells

__Abstract__ The plasma membrane of mammalian cells is formed by two layers of lipids (lipid bilayer), primarily phospholipids, glycolipids and cholesterol, in which many different proteins are embedded. Phospholipid consists of a glycerol backbone esterified to fatty acids (the "lipid tail") and, via a phosphate group, to either choline, serine, inositol or ethanolamine (the "head group"). Whereas the head group is hydrophilic and oriented towards the outer surface of the membrane, the lipid tail is hydrophobic and pointed towards the inner part. The plasma membrane is impermeable to large molecules like carbohydrates and proteins but readily permeable to small uncharged molecules like oxygen, water, and carbon dioxide. Molecules can move through the membrane either by direct diffusion or through specialized channels or transport proteins (facilitated diffusion). In an isolated system, as stated by the Second Law of Thermodynamics, all events move spontaneously from a higher energy state to a lower energy state and are driven by the tendency to increase the entropy (degree for randomness/ disorder). When molecules are evenly distributed throughout the available space, the entropy is at its maximum. Therefore, free moving molecules and atoms (i.e. not part of a crystal structure and not restrained by additional forces) tend to distribute themselves over an as large as possible area. As a consequence of the Second Law of Thermodynamics, differences in the concentrations of non-permeable solutes between the cell and its surrounding medium will result in a redistribution of the solvent (e.g. water) to maintain the lowest energy possible, a phenomenon known as osmosis. Therefore, in response to an osmotic imbalance, water will move across a semi-permeable membrane until the water molecules are equally distributed, resulting in swelling or shrinkage. The Gibbs-Don nan effect refers to the observation that under certain conditions charged molecules or ions fail to distribute evenly across a semi-permeable membrane. At the Gibbs-Donnan equilibrium, the total number of positive charges balanced the total number of negative charges (bulk electroneutrality). Due to the presence of charged membrane-impermeable macromolecules and the electrogenic Na+ /K+ pump, however, the Gibbs Donnan equilibrium will never be obtained in an intact cell, leading to an asymmetric distribution of permeable ions and the generation of the membrane potential. A consequence of the presence of negatively charged membrane-impermeable proteins is the constant tendency of cells to accumulate water. To counteract a potential increase in volume, sodium is removed from the cells by the Na+ /K+ pump on the expenditure of metabolic energy. Because alterations in cell volume may affect many biochemical and physiological processes, almost all cell types have additional mechanisms to regulate their volume and to limit or prevent swelling and shrinkage

Preliminary study on phytoliths identification in two major riverbanks of Selangor (Gombak and Klang riverbanks)

Phytoliths are plant fossils found within the plant cells of embryophytes and it can be deposited into the uppermost horizon of the soil when embryophytes die and decay. This will cause the phytoltihs is released from its organic matrix and chemisorbed into the soil particles. This study aimed to determine the presence and morphology of phytoliths found in two major riverbanks of Selangor (Gombak and Klang riverbanks). Composite soil samples were collected from the top two cm of the soil of Gombak and Klang riverbanks with each composite consists of five subsamples. The distance between each subsample is two m apart. The composite soil samples were subjected to extraction process before phytoliths isolation which involved deflocculation using 5% of sodium hexametaphosphate, decarbonation using 10% hydrochloric acid, organic material removal using 65% nitric acid and potassium chlorate, clay removal via centrifuge sedimentation and, organic matter and humic colloids removal using 10% potassium hydroxide. Heavy liquid zinc bromide/hydrochloric acid was used to isolate phytoliths. The presence and morphology of phytoliths between the two riverbanks were identified and counted using comparison microscope. The results were compared between the two riverbanks to determine if discrimination of soil in different site is possible

RFID in the warehouse:a literature analysis (1995-2010) of its applications, benefits, challenges and future trends

Radio Frequency Identification (RFID) has been identified as a crucial technology for the modern 21st century knowledge-based economy. Some businesses have realised benefits of RFID adoption through improvements in operational efficiency, additional cost savings, and opportunities for higher revenues. RFID research in warehousing operations has been less prominent than in other application domains. To investigate how RFID technology has had an impact in warehousing, a comprehensive analysis of research findings available from articles through leading scientific article databases has been conducted. Articles from years 1995 to 2010 have been reviewed and analysed with respect to warehouse operations, RFID application domains, benefits achieved and obstacles encountered. Four discussion topics are presented covering RFID in warehousing focusing on its applications, perceived benefits, obstacles to its adoption and future trends. This is aimed at elucidating the current state of RFID in the warehouse and providing insights for researchers to establish new research agendas and for practitioners to consider and assess the adoption of RFID in warehousing functions

Improved planar InAs avalanche photodiodes with reduced dark current and increased responsivity

Indium Arsenide (InAs) infrared photodiodes provide high quantum efficiency in the wavelength range of 1.0-3.0 μm. Planar diode configuration has been adopted to reduce surface leakage. In this work, new fabrication procedures for planar InAs avalanche photodiodes (APDs) are reported. Beryllium (Be) ions were implanted into InAs at a relatively low energy of 34 keV. Effects of duration of post implant annealing on the electrical characteristics of InAs APDs were investigated. It was found that a combination of post implant annealing at 500 °C for 15 min and a shallow surface etch produces planar APDs with good characteristics (room temperature dark current density of 0.52 A/cm 2 at -0.2 V and external quantum efficiency of 51% at 1520 nm at -0.3 V). These represent a 3 times reduction in dark current and 1.4 times increase in responsivity, compared to earlier Be-implanted planar InAs APDs. The APDs' avalanche gain characteristics remain similar to those from earlier reports, with a gain of 4 at a relatively low operating bias of 5 V. This suggests the potential of integrating InAs APDs with low voltage readout integrated circuits (ROIC) for development of infrared imaging arrays. The data reported in this paper is available from the ORDA digital repository (DOI: 10.15131/shef.data.6955037)

Entanglement preparation using symmetric multiports

We investigate the entanglement produced by a multi-path interferometer that is composed of two symmetric multiports, with phase shifts applied to the output of the first multiport. Particular attention is paid to the case when we have a single photon entering the interferometer. For this situation we derive a simple condition that characterize the types of entanglement that one can generate. We then show how one can use the results from the single photon case to determine what kinds of multi-photon entangled states one can prepare using the interferometer.Comment: 6 pages, 2 figures, accepted for publication in European Journal of Physics

Entanglement preparation using symmetric multiports

We investigate the entanglement produced by a multi-path interferometer that is composed of two symmetric multiports, with phase shifts applied to the output of the first multiport. Particular attention is paid to the case when we have a single photon entering the interferometer. For this situation we derive a simple condition that characterize the types of entanglement that one can generate. We then show how one can use the results from the single photon case to determine what kinds of multi-photon entangled states one can prepare using the interferometer.Comment: 6 pages, 2 figures, accepted for publication in European Journal of Physics

Electrical and optical characterisation of low temperature grown InGaAs for photodiode applications

Dilute bismide and nitride alloys are promising semiconductors for bandgap engineering, opening additional design freedom for devices such as infrared photodiodes. Low growth temperatures are required to incorporate bismuth or nitrogen into III V semiconductors. However, the effects of low growth temperature on dark current and responsivity are not well understood. In this work, a set of InGaAs p i n wafers were grown at a constant temperature of 250, 300, 400 and 500 °C for all p, i and n layers. A second set of wafers was grown where the p and n layers were grown at 500 °C while the i-layers were grown at 250, 300 and 400 °C. Photodiodes were fabricated from all seven wafers. When constant growth temperature was employed (for all p, i and n layers), we observed that photodiodes grown at 500 °C show dark current density at 1 V that is 6 orders of magnitude lower while the responsivity at an illumination wavelength of 1520 nm is 4.5 times higher than those from photodiodes grown at 250 °C. Results from the second set of wafers suggest that performance degradation can be recovered by growing the p and n layers at high temperature. For instance, comparing photodiodes with i-layers grown at 250 °C, photodiodes showed dark current density at -1 V that is 5 orders of magnitude lower when the p and n layer were grown at 500 °C. Postgrowth annealing, at 595 °C for 15 minutes, on the two wafers grown at 250 and 300 °C showed recovery of diode responsivity but no significant improvement in the dark current. Our work suggests that growth of the cap layer at high temperature is necessary to maintain the responsivity and minimise the dark current degradation, offering a pathway to developing novel photodiode materials that necessitate low growth temperatures

B_c meson rare decays in the light-cone quark model

We investigate the rare decays $B_c \rightarrow D_s(1968) \ell \bar{\ell}$ and $B_c\rightarrow D_s^*(2317) \ell \bar{\ell}$ in the framework of the light-cone quark model (LCQM). The transition form factors are calculated in the space-like region and then analytically continued to the time-like region via exponential parametrization. The branching ratios and longitudinal lepton polarization asymmetries (LPAs) for the two decays are given and compared with each other. The results are helpful to investigating the structure of $B_c$ meson and to testing the unitarity of CKM quark mixing matrix. All these results can be tested in the future experiments at the LHC.Comment: 9 pages, 11 figures, version accepted for publication in EPJ