Measurement of the generalized polarizabilities of the proton in virtual Compton scattering at Q2=0.92 and 1.76 GeV2

We report a virtual Compton scattering study of the proton at low c.m. energies. We have determined the structure functions P(LL)-P(TT)/epsilon and P(LT), and the electric and magnetic generalized polarizabilities (GPs) alpha(E)(Q2) and beta(M)(Q2) at momentum transfer Q(2)=0.92 and 1.76 GeV2. The electric GP shows a strong falloff with Q2, and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a falloff; this can be interpreted as the dominance of a long-distance diamagnetic pion cloud at low Q2, compensated at higher Q2 by a paramagnetic contribution from piN intermediate states.     

Integration of a macro/micro architectured compartmentalised neuronal culture device using a rapid prototyping moulding process

The rapid prototyping of a reversible and one step moulded compartmentalised neuron glass/PDMS device with a thin wall barrier directly adjacent to the reservoirs is presented. A simple moulding technique to produce these devices results in a barrier of 560 μm where the 3 μm deep by 8 μm wide channels can be reversibly fabricated in either the glass base or PDMS compartmentalised mould depending on the type of application required. Using glass substrates with commercially laser engraved microchannels, both the PDMS planar and PDMS channelled device can be easily fabricated in a standard laboratory. The compartmentalised device has several advantages including good experimental accessibility and versatility with a variety of end user applications.     

Indirect fluorescence detection of phenolic compounds by capillary electrophoresis on a glass device

A micromachined capillary electrophoresis system has been fabricated on a glass device for the separation and indirect fluorescence detection of phenols. Using this device two phenols viz., 2,4-dichlorophenol and pentachlorophenol, were separated within 12 s compared to under 19 min on a conventional capillary electrophoresis system using direct ultraviolet detection. The precision of the glass device ranged from 12.7%–16.7% compared to 0.42%–4.9% for the conventional system. Both systems showed good linearity in the concentration range of 0.8– 6.38 mM for the glass device and 5–130 μM for the conventional system. The relationship between temperature and high voltage with baseline drift was also investigated. These results provide a foundation for the development of a miniaturised chemical analysis system for the on-line analysis of phenols in water. Received: 24 January 2000 / Revised: 27 March 2000 / Accepted: 29 March 2000     

Individually addressable microelectrode array for monitoring oxygen and nitric oxide release

We have fabricated a six individual addressable gold working electrode microarray. The device is wirebonded to an eight-pin DIL package that can be easily interconnected to an external multi-channel potentiostat. A polyion complex film coating on the electrode surface provides a suitable coating for the growth of cells. The responses of oxygen and nitric oxide were assessed on uncoated and coated devices using electroanalytical methods. The film coating reduced the diffusion current by approximately 20% in both cases. No changes in the electrochemical mechanism were observed. Simultaneous recordings were obtained for 2 h in the presence of the cells, thus the device is stable for the duration of the bioanalytical measurements. Measurements were conducted to study the simultaneous changes in oxygen and nitric oxide levels in cultured fibroblast cells in the presence of growth hormones that cause cell proliferation. Increases in oxygen consumption of the cells were coupled with increases in nitric oxide levels when in the presence of the growth hormones. Use of a biological detergent to cause an oxidative burst resulted in a large increase in the current for potentials set to detect nitric oxide and oxygen.     

Electrokinetic DNA transport in 20 nm-high nanoslits: evidence for movement through a wall-adsorbed

The electrokinetic transport behavior of λ-DNA (48 kbp) in 20 nm-high fused-silica nanoslits in the presence of short-chain PVP is investigated. Mobility and video data show a number of phenomena that are typical of DNA transport through gels or polymer solutions, thus indicative of rigid migration obstacles in the DNA pathway. Calculations show that a several nanometer thin layer of wall-adsorbed PVP ('nano-gel') can provide such a rigid obstacle matrix to the DNA. Such ultrathin wall-adsorbed polymer layers represent a new type of matrix for electrokinetic DNA separation.     

Pinning and avalanches in hydrophobic microchannels

Rare events appear in a wide variety of phenomena such as rainfall, floods, earthquakes, and risk. We demonstrate that the stochastic behavior induced by the natural roughening present in standard microchannels is so important that the dynamics for the advancement of a water front displacing air has plenty of rare events. We observe that for low pressure differences the hydrophobic interactions of the water front with the walls of the microchannel put the front close to the pinning point. This causes a burstlike dynamics, characterized by series of pinning and avalanches, that leads to an extreme-value Gumbel distribution for the velocity fluctuations and a nonclassical time exponent for the advancement of the mean front position as low as 0.38.     

Interconnected reversible lab-on-a-chip technology

Interconnected lab-on-a-chip modules with minimal dead volume have been developed resulting in the 'plug and play' concept based upon a reversible bonding process. This paper describes the detail of a chip to chip interconnection method, where devices have been aligned and bonded within 15 min and rapidly disassembled in under 5 min. The transport of fluorescein between the chip modules was used as a model microfluidic system and analysed in order to demonstrate the electrophoretic performance of the device and the interconnected junction. Using this technology, in the future different modules for various applications can be developed and interconnected, depending on the required applications. In addition, this simple but rapid method of chip to chip connection overcomes potential problems associated with integrating incompatible materials on one device.     

Indirect fluorescence detection of phenolic compounds by capillary electrophoresis on a glass device

A micromachined capillary electrophoresis system has been fabricated on a glass device for the separation and indirect fluorescence detection of phenols. Using this device two phenols viz., 2,4-dichlorophenol and pentachlorophenol, were separated within 12 s compared to under 19 min on a conventional capillary electrophoresis system using direct ultraviolet detection. The precision of the glass device ranged from 12.7%-16.7% compared to 0.42%-4.9% for the conventional system. Both systems showed good linearity in the concentration range of 0.8-6.38 mM for the glass device and 5-130 microM for the conventional system. The relationship between temperature and high voltage with baseline drift was also investigated. These results provide a foundation for the development of a miniaturised chemical analysis system for the on-line analysis of phenols in water.     

Transport coefficients of argon,nitrogen, oxygen,argon-nitrogen,and argon-oxygen plasmas

Calculated values of the viscosity, thermal conductivity, and electrical conductivity of argon, nitrogen, and oxygen plasmas, and mixtures of argon anti nitrogen and of argon anti oxygen, are presented. In addition, combined ordinary, pressure, and thermal diffusion coefficients are given for the gas mixtures. These three combined diffusion coefficients fully describe di fusion of the two gases, irrespective of their degree of dissociation or ionizati on. The calculations, which assume local thermodynamic equilibrium, are performed! for atmospheric-pressure plasmas in the temperature range /torn 300 to 30,000 K. A number of the collision integrals used in calculating the transport coefficients are significantly more accurate than values used in previous theoretical studies, resulting in more reliable values of the transport coefficients. The results are compared with those of published theoretical and experimental studies.