Modelling nematohydrodynamics in liquid crystal devices

We formulate a lattice Boltzmann algorithm which solves the hydrodynamic equations of motion for nematic liquid crystals. The applicability of the approach is demonstrated by presenting results for two liquid crystal devices where flow has an important role to play in the switching.Comment: 6 pages including 5 figure

Web-based interface system for bedside monitor

From face-to-face consultation to medicine at a distance, technology is changing the way medical services are delivered to the people. We are going into an era where the information is being digitized to be stored in a database. This is done in order to reduce information overlap and redundancy that are the main problems the health care sector are facing right now. More hospitals in other more advanced countries are going paperless. In order to provide better services to the critically ill patients in the ICU or CCU, a data acquisition program is developed for the acquisition of vital signs monitored in the critical care units. This work discusses the work done in extracting the data and signal from patient monitor BSM 8800 to the computer. The data are acquired using RS232C Interface Protocol. The vital signs acquired include oxygen saturation (SaCh), heart rate (HR), electrocardiograph (ECG) signal, non-invasive blood pressure (NIBP), respiration rate (RR), temperature (TEMP) and end tidal carbon dioxide (PETCO2 or ETCO2). Ventricular Premature Contraction (VPC), ST level and arrhythmia information are also acquired and displayed to provide a more thorough information on the condition of the patients. Alarm detection is also programmed so that in critical conditions the vital signs will be displayed in red for extra caution. An ECG user control is designed and embedded in the web page in order to convert and plot the ECG waveform from hexadecimal values sent from the bedside monitor. The user control has been tested its accuracy and proved its validity to reconstruct the original ECG waveform. Basic patient information can also be seen from the graphical user interface (GUI) that has been developed. Physicians and medical practitioners have to register with the system before gaining access to the system and only the physician-in-charge of the patient can see the more intricate details of the patient

Lipid Ion Channels

The interpretation electrical phenomena in biomembranes is usually based on the assumption that the experimentally found discrete ion conduction events are due to a particular class of proteins called ion channels while the lipid membrane is considered being an inert electrical insulator. The particular protein structure is thought to be related to ion specificity, specific recognition of drugs by receptors and to macroscopic phenomena as nerve pulse propagation. However, lipid membranes in their chain melting regime are known to be highly permeable to ions, water and small molecules, and are therefore not always inert. In voltage-clamp experiments one finds quantized conduction events through protein-free membranes in their melting regime similar to or even undistinguishable from those attributed to proteins. This constitutes a conceptual problem for the interpretation of electrophysiological data obtained from biological membrane preparations. Here, we review the experimental evidence for lipid ion channels, their properties and the physical chemistry underlying their creation. We introduce into the thermodynamic theory of membrane fluctuations from which the lipid channels originate. Furthermore, we demonstrate how the appearance of lipid channels can be influenced by the alteration of the thermodynamic variables (temperature, pressure, tension, chemical potentials) in a coherent description that is free of parameters. This description leads to pores that display dwell times closely coupled to the fluctuation lifetime via the fluctuation-dissipation theorem. Drugs as anesthetics and neurotransmitters are shown to influence the channel likelihood and their lifetimes in a predictable manner. We also discuss the role of proteins in influencing the likelihood of lipid channel formation.Comment: Revie

Hydrogen bonding structure of confined water templated by a metal-organic framework with open metal sites.

Water in confinement exhibits properties significantly different from bulk water due to frustration in the hydrogen-bond network induced by interactions with the substrate. Here, we combine infrared spectroscopy and many-body molecular dynamics simulations to probe the structure and dynamics of confined water as a function of relative humidity within a metal-organic framework containing cylindrical pores lined with ordered cobalt open coordination sites. Building upon the agreement between experimental and theoretical spectra, we demonstrate that water at low relative humidity binds initially to open metal sites and subsequently forms disconnected one-dimensional chains of hydrogen-bonded water molecules bridging between cobalt atoms. With increasing relative humidity, these water chains nucleate pore filling, and water molecules occupy the entire pore interior before the relative humidity reaches 30%. Systematic analysis of rotational and translational dynamics indicates heterogeneity in this pore-confined water, with water molecules displaying variable mobility as a function of distance from the interface

Single-molecule spectroscopic studies of conjugated polymers

A semiconductor is a type of material which has electrical properties in between an insulator and a conductor. A conductor can be thought of as a group of atoms surrounded by a sea of free electrons, which are free to move throughout the material; in contrast, the electrons in an insulator are tightly localized on a specific atom or molecule. In a semiconductor, the electrons are localized as in insulators; however, with the addition of energy, the electrons in semiconductors are easily excited into a state where they are free to move throughout the material as in a conductor. Thus, with the proper combination of materials, electrons can flow from the semiconductor into a circuit when light strikes it. This is the basis behind solar energy, in which a current is generated when sunlight hits silicon-based panels known as photovoltaic cells. Materials known as conjugated organic polymers are semiconductors made up of elements like carbon, hydrogen, and nitrogen. A polymer is a chain of small repeated units known as monomers. In a conjugated polymer, the electrons of the molecule are shared across several atoms in the polymer; when these electrons are excited, they are then free to move essentially along the entire length of the polymer. Theoretically, then, conjugated polymers could be used for applications like solar energy, as well. In order to study single conjugated polymer molecules, a technique known as singlemolecule spectroscopy (SMS) was used. In SMS, light from a laser is focused to a very small spot ( 10 nm) on a sample composed of individual, isolated single molecules. This laser light excites electrons in the molecules; when the electrons relax back to their ground (lowest-energy) state, they re-release the energy as a characteristic group of wavelengths of light known as a spectrum. I studied the spectroscopy of the conjugated polymers F8BT and MEH-PPV. For F8BT, I studied the effect of polymer size and temperature on the fluorescence of the polymer. The spectrum of F8BT displays a bimodal distribution: some molecules have a peak in their emission spectrum at approximately 570 nm (“red”), while some have it at 530 nm (“blue”). This bimodal distribution collapses at low temperatures to a single emission peak. Furthermore, small F8BT molecules emit almost entirely in the blue, while many more large F8BT molecules emit in the red form. This indicates that there is some type of low-energy electron “trap” that becomes more abundant as the polymer gets larger. The most commonly-proposed mechanism for this trap is contact between different parts of the polymer chain. For MEH-PPV, I studied 100-molecule aggregates of MEH-PPV polymers. These aggregates contain enough molecules to display characteristics of bulk MEH-PPV with on the order of 1023 molecules, but are small enough to be essentially homogeneous – that is, all of the molecules within a single aggregate have identical environments. MEHPPV shows a similar bimodal emission distribution to that of F8BT; the aggregates emit almost exclusively in the “red” form of MEH-PPV. This further supports the hypothesis that chain-chain contact makes a large contribution to the formation of low-energy traps. Solar energy production is just one of many areas where conjugated polymers such as F8BT and MEH-PPV could have a huge impact on the world. If good efficiencies can be achieved in converting sunlight into electrical current, things like photovoltaic cells could be much cheaper, easier to produce, and more environmentally friendly.Chemistr