Modeling of Heat Transfer in Microchannel Gas Flow

Due to the existence of a velocity slip and temperature jump on the solid walls, the heat transfer in microchannels significantly differs from the one in the macroscale. In our research, we have focused on the pressure driven gas flows in a simple finite microchannel geometry, with an entrance and an outlet, for low Reynolds (Re<200) and low Knudsen (Kn<0.01) numbers. For such a regime, the slip induced phenomena are strongly connected with the viscous effects. As a result, heat transfer is also significantly altered. For the optimization of flow conditions, we have investigated various temperature gradient configurations, additionally changing Reynolds and Knudsen numbers. The entrance effects, slip flow, and temperature jump lead to complex relations between flow behavior and heat transfer. We have shown that slip effects are generally insignificant for flow behavior. However, two configuration setups (hot wall cold gas and cold wall hot gas) are affected by slip in distinguishably different ways. For the first one, which concerns turbomachinery, the mass flow rate can increase by about 1% in relation to the no-slip case, depending on the wall-gas temperature difference. Heat transfer is more significantly altered. The Nusselt number between slip and no-slip cases at the outlet of the microchannel is increased by about 10%.

Disruption of the histidine triad nucleotide-binding hint2 gene in mice affects glycemic control and mitochondrial function

The histidine triad nucleotide-binding (Hint2) protein is a mitochondrial adenosine phosphoramidase expressed in liver and pancreas. Its physiological function is unknown. To elucidate the role of Hint2 in liver physiology, the Hint2 gene was deleted. Hint2(-/-) and Hint2(+/+) mice were generated in a mixed C57Bl6/J x 129Sv background. At 20 weeks, the phenotypic changes in Hint2(-/-) relative to Hint2(+/+) mice were an accumulation of hepatic triglycerides, decreased tolerance to glucose, a defective counter-regulatory response to insulin-provoked hypoglycaemia, an increase in plasma interprandial insulin but a decrease in glucose stimulated insulin secretion and defective thermoregulation upon fasting. Leptin mRNA in adipose tissue and plasma leptin were elevated. In mitochondria from Hint2(-/-) hepatocytes, state 3 respiration was decreased, a finding confirmed in HepG2 cells where HINT2 mRNA was silenced. The linked complex II to III electron transfer was decreased in Hint2(-/-) mitochondria, which was accompanied by a lower content of coenzyme Q. HIF-2α expression and the generation of reactive oxygen species were increased. Electron microscopy of mitochondria in Hint2(-/-) mice aged 12 months revealed clustered, fused organelles. The hepatic activities of 3-hydroxyacyl-CoA dehydrogenase short chain and glutamate dehydrogenase (GDH) were decreased by 68% and 60%, respectively, without a change in protein expression. GDH activity was similarly decreased in HINT2-silenced HepG2 cells. When measured in the presence of purified sirtuin 3, latent GDH activity was recovered (126% in Hint2(-/-) vs. 83% in Hint2(+/+) ). This suggests a greater extent of acetylation in Hint2(-/-) than in Hint2(+/+) . Conlusions: Hint2 positively regulates mitochondrial lipid metabolism and respiration, and glucose homeostasis. The absence of Hint2 provokes mitochondrial deformities and a change in the pattern of acetylation of selected proteins. (HEPATOLOGY 2012.).

Generalized eMC implementation for Monte Carlo dose calculation of electron beams from different machine types

The electron Monte Carlo (eMC) dose calculation algorithm available in the Eclipse treatment planning system (Varian Medical Systems) is based on the macro MC method and uses a beam model applicable to Varian linear accelerators. This leads to limitations in accuracy if eMC is applied to non-Varian machines. In this work eMC is generalized to also allow accurate dose calculations for electron beams from Elekta and Siemens accelerators. First, changes made in the previous study to use eMC for low electron beam energies of Varian accelerators are applied. Then, a generalized beam model is developed using a main electron source and a main photon source representing electrons and photons from the scattering foil, respectively, an edge source of electrons, a transmission source of photons and a line source of electrons and photons representing the particles from the scrapers or inserts and head scatter radiation. Regarding the macro MC dose calculation algorithm, the transport code of the secondary particles is improved. The macro MC dose calculations are validated with corresponding dose calculations using EGSnrc in homogeneous and inhomogeneous phantoms. The validation of the generalized eMC is carried out by comparing calculated and measured dose distributions in water for Varian, Elekta and Siemens machines for a variety of beam energies, applicator sizes and SSDs. The comparisons are performed in units of cGy per MU. Overall, a general agreement between calculated and measured dose distributions for all machine types and all combinations of parameters investigated is found to be within 2% or 2 mm. The results of the dose comparisons suggest that the generalized eMC is now suitable to calculate dose distributions for Varian, Elekta and Siemens linear accelerators with sufficient accuracy in the range of the investigated combinations of beam energies, applicator sizes and SSDs.

Modulation of human CYP19A1 activity by mutant NADPH P450 oxidoreductase

Mutations in NADPH P450 oxidoreductase (POR) cause a broad spectrum of human disease with abnormalities in steroidogenesis. We have studied the impact of P450 reductase mutations on the activity of CYP19A1. POR supported CYP19A1 activity with a calculated Km of 126 nm for androstenedione and a Vmax of 1.7 pmol/min. Mutations R457H and V492E located in the FAD domain of POR that disrupt electron transfer caused a complete loss of CYP19A1 activity. The A287P mutation of POR decreased the activities of CYP17A1 by 60-80% but had normal CYP19A1 activity. Molecular modeling and protein docking studies suggested that A287P is involved in the interaction of POR:CYP17A1 but not in the POR:CYP19A1 interaction. Mutations C569Y and V608F in the NADPH binding domain of POR had 49 and 28% of activity of CYP19A1 compared with normal reductase and were more sensitive to the amount of NADPH available for supporting CYP19A1 activity. Substitution of NADH for NADPH had a higher impact on C569Y and V608F mutants of POR. Similar effects were obtained at low/high (5.5/8.5) pH, but using octanol to limit the flux of electrons from POR to CYP19A1 inhibited activity supported by all variants. High molar ratios of KCl also reduced the CYP19A1 supporting activities of C569Y and V608F mutants of POR to a greater extent compared to normal POR and A287P mutant. Because POR supports many P450s involved in steroidogenesis, bone formation, and drug metabolism, variations in the effects of POR mutations on specific enzyme activities may explain the broad clinical spectrum of POR deficiency.

Controlling electronic and magnetic properties of ultra narrow multilayered nanowires

Interest in the study of magnetic/non-magnetic multilayered structures took a giant leap since Grünberg and his group established that the interlayer exchange coupling (IEC) is a function of the non-magnetic spacer width. This interest was further fuelled by the discovery of the phenomenal Giant Magnetoresistance (GMR) effect. In fact, in 2007 Albert Fert and Peter Grünberg were awarded the Nobel Prize in Physics for their contribution to the discovery of GMR. GMR is the key property that is being used in the read-head of the present day computer hard drive as it requires a high sensitivity in the detection of magnetic field. The recent increase in demand for device miniaturization encouraged researchers to look for GMR in nanoscale multilayered structures. In this context, one dimensional(1-D) multilayerd nanowire structure has shown tremendous promise as a viable candidate for ultra sensitive read head sensors. In fact, the phenomenal giant magnetoresistance(GMR) effect, which is the novel feature of the currently used multilayered thin film, has already been observed in multilayered nanowire systems at ambient temperature. Geometrical confinement of the supper lattice along the 2-dimensions (2-D) to construct the 1-D multilayered nanowire prohibits the minimization of magnetic interaction- offering a rich variety of magnetic properties in nanowire that can be exploited for novel functionality. In addition, introduction of non-magnetic spacer between the magnetic layers presents additional advantage in controlling magnetic properties via tuning the interlayer magnetic interaction. Despite of a large volume of theoretical works devoted towards the understanding of GMR and IEC in super lattice structures, limited theoretical calculations are reported in 1-D multilayered systems. Thus to gauge their potential application in new generation magneto-electronic devices, in this thesis, I have discussed the usage of first principles density functional theory (DFT) in predicting the equilibrium structure, stability as well as electronic and magnetic properties of one dimensional multilayered nanowires. Particularly, I have focused on the electronic and magnetic properties of Fe/Pt multilayered nanowire structures and the role of non-magnetic Pt spacer in modulating the magnetic properties of the wire. It is found that the average magnetic moment per atom in the nanowire increases monotonically with an ~1/(N(Fe)) dependance, where N(Fe) is the number of iron layers in the nanowire. A simple model based upon the interfacial structure is given to explain the 1/(N(Fe)) trend in magnetic moment obtained from the first principle calculations. A new mechanism, based upon spin flip with in the layer and multistep electron transfer between the layers, is proposed to elucidate the enhancement of magnetic moment of Iron atom at the Platinum interface. The calculated IEC in the Fe/Pt multilayered nanowire is found to switch sign as the width of the non-magnetic spacer varies. The competition among short and long range direct exchange and the super exchange has been found to play a key role for the non-monotonous sign in IEC depending upon the width of the Platinum spacer layer. The calculated magnetoresistance from Julliere's model also exhibit similar switching behavior as that of IEC. The universality of the behavior of exchange coupling has also been looked into by introducing different non-magnetic spacers like Palladium, Copper, Silver, and Gold in between magnetic Iron layers. The nature of hybridization between Fe and other non-magnetic spacer is found to dictate the inter layer magnetic interaction. For example, in Fe/Pd nanowire the d-p hybridization in two spacer layer case favors anti-ferromagnetic (AFM) configuration over ferromagnetic (FM) configuration. However, the hybridization between half-filled Fe(d) and filled Cu(p) state in Fe/Cu nanowire favors FM coupling in the 2-spacer system.

Manipulation of energy transfer processes in nanochannels

The realisation of molecular assemblies featuring specific macroscopic properties is a prime example for the versatility of supramolecular organisation. Microporous materials such as zeolite L are well suited for the preparation of host-guest composites containing dyes, complexes, or clusters. This short tutorial focuses on the possibilities offered by zeolite L to study and influence Förster resonance energy transfer inside of its nanochannels. The highly organised host-guest materials can in turn be structured on a larger scale to form macroscopic patterns, making it possible to create large-scale structures from small, highly organised building blocks for novel optical applications.

Two-dimensional assembly and local redox-activity of molecular hybrid structures in an electrochemical environment

The self-assembly and redox-properties of two viologen derivatives, N-hexyl-N-(6-thiohexyl)-4,4-bipyridinium bromide (HS-6V6-H) and N,N-bis(6-thiohexyl)-4,4-bipyridinium bromide (HS-6V6-SH), immobilized on Au(111)-(1x1) macro-electrodes were investigated by cyclic voltammetry, surface enhanced infrared spectroscopy (SEIRAS) and in situ scanning tunneling microscopy (STM). Depending on the assembly conditions one could distinguish three different types of adlayers for both viologens: a low coverage disordered and an ordered striped phase of flat oriented molecules as well as a high coverage monolayer composed of tilted viologen moieties. Both molecules, HS-6V6-H and HS-6V6-SH, were successfully immobilized on Au(poly) nano-electrodes, which gave a well-defined redox-response in the lower pA–current range. An in situ STM configuration was employed to explore electron transport properties of single molecule junctions Au(T)|HS-6V6-SH(HS-6V6-H)|Au(S). The observed sigmoidal potential dependence, measured at variable substrate potential ES and at constant bias voltage (ET–ES), was attributed to electronic structure changes of the viologen moiety during the one-electron reduction/re-oxidation process V2+ V+. Tunneling experiments in asymmetric, STM-based junctions Au(T)-S-6V6-H|Au(S) revealed current (iT)–voltage (ET) curves with a maximum located at the equilibrium potential of the redox-process V2+ V+. The experimental iT–ET characteristics of the HS-6V6-H–modified tunneling junction were tentatively attributed to a sequential two-step electron transfer mechanism.

An in-situ surface electrochemistry approach toward whole-cell studies: Charge transfer between Geobacter sulfurreducens and electrified metal/electrolyte interfaces through linker molecules

Electrochemical reactivity and structure properties of electrogenic bacteria, Geobacter sulfurreducens (Gs) were studied to explore the heterogeneous electron transfer at the bacteria/electrode interface using electrochemical and in-situ spectroscopic techniques. The redox behavior of Gs adsorbed on a gold electrode, which is modified with a ω-functionalized self-assembled monolayer (SAM) of alkanethiols, depends strongly on the terminal group. The latter interacts directly with outermost cytochromes embedded into the outer membrane of the Gs cells. The redox potential of bacterial cells bound electrostatically to a carboxyl-terminated SAM is close to that observed for bacteria attached to a bare gold electrode, revealing a high electronic coupling at the cell/SAM interface. The redox potentials of bacterial cells adsorbed on amino- and pyridyl-terminated SAMs are significantly different suggesting that the outermost cytochromes changes their conformation upon adsorption on these SAMs. No redox activity of Gs was found with CH3-, N(CH3)3+- and OH-terminated SAMs. Complementary in-situ spectroscopic studies on bacteria/SAMs/Au electrode assemblies were carried out to monitor structure changes of the bacterial cells upon polarization. Spectro-electrochemical techniques revealed the electrochemical turnover of the oxidized and reduced states of outer membrane cytochromes (OMCs) in Gs, providing evidence that the OMCs are responsible for the direct electron transfer to metal electrodes, such as gold or silver, during the electricity production. Furthermore, we observed spectroscopic signatures of the native structure of the OMCs and no conformational change during the oxidation/reduction process of the microorganisms. These findings indicate that the carboxyl-anchoring group provides biocompatible conditions for the outermost cytochromes of the Gs, which facilitate the heterogeneous electron transfer at the microorganism/electrode interface.

Synthesis and Redox and Photophysical Properties of Benzodifuran-Spiropyran Ensembles

Two benzodifuran (BDF)-coupled spiropyran (SP) systems and their BDF reference compounds were obtained in good yields through HuisgenMeldalSharpless click chemistry and then subjected to investigation of their electrochemical and photophysical properties. In both SP and merocyanine (MC) forms of the coupled molecules, the BDF-based emission is quenched to around 1 of the quantum yield of emission from the BDF reference compounds. Based on electrochemical data, this quenching is attributed to oxidative electron-transfer quenching. Irradiation at 366nm results in ring opening to the MC forms of the BDF-coupled SP compounds and the SP reference compound with a quantum efficiency of about 50. The rate constants for the thermal ring closing are approximately 3.4x103s1. However, in the photostationary states the MC fractions of the coupled molecules are substantially lower than that of the reference SP compound, attributed to the observed acceleration of the ring-closing reaction upon irradiation. As irradiation at 366nm invariably also excites higher-energy transitions of the BDF units in the coupled compounds, the ring-opening reaction is accelerated relative to the SP reference, which results in lower MC fractions in the photostationary state. Reversible photochromism of these BDF-coupled SP compounds renders them promising in the field of molecular switches.

Implementation of a virtual correlative light and transmission electron microscope

In the long run, the widespread use of slide scanners by pathologists requires an adaptation of teaching methods in histology and cytology in order to target these new possibilities of image processing and presentation via the internet. Accordingly, we were looking for a tool with the possibility to teach microscopic anatomy, histology, and cytology of tissue samples which would be able to combine image data from light and electron microscopes independently of microscope suppliers. With the example of a section through the villus of jejunum, we describe here how to process image data from light and electron microscopes in order to get one image-stack which allows a correlation of structures from the microscopic anatomic to the cytological level. With commercially available image-presentation software that we adapted to our needs, we present here a platform which allows for the presentation of this new but also of older material independently of microscope suppliers.

Studies on the interaction of NADPH cytochrome P-450 reductase and cytochromes P-450

Chemical modification of cytochrome P-450 reductase was used to determine the involvement of charged amino acids in the interaction between the reductase and two forms of cytochrome P-450. Acetylation of 11 lysine residues of the reductase with acetic anhydride yielded a 20-40% decrease in the K$\sb{\rm m}$ of the reductase for cytochrome P-450b or cytochrome P-450c. Modification of carboxyl groups on the reductase with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and methylamine, glycine methyl ester, or taurine as nucleophiles inhibited the interaction with the cytochromes P-450. We were able to modify 4.0, 7.9, and 5.9 carboxyl groups using methylamine, glycine methyl ester, and taurine, respectively. The apparent K$\sb{\rm m}$ for cytochrome P-450c or cytochrome P-450b was increased 1.3 to 5.2 fold. There were varied effects on the V$\sb{\rm max}$. There was no significant change in the conformation of the reductase upon chemical modification. These results strongly suggest that electrostatic interactions as well as steric constraints play a role in the binding and electron transfer step(s) between the reductase and cytochrome P-450. Cytochrome P-450 protected 0.8 moles of carboxyl residues on the reductase from being modified with EDC. These protected amino acids on the reductase are presumably involved in binding to cytochrome P-450. The specific peptide containing these amino acids has been identified. ^

The role of menaquinone in the nitrate reductase complex

Membrane bound, respiratory nitrate reductase in Escherichia coli is composed of three subunits, αβγ. The active complex is anchored to the membrane by membrane-integrated γ subunit and can reduce nitrate to nitrite with membrane quinones, (ubiquinone or menaquinone) as physiological electron donors. The transfer of electrons through the complex is thought to involve the sequence: membrane quinols → b-type hemes (γ subunit) → Fe-S centers (β subunit) → molybdopterin (α subunit) → nitrate. The enzyme can be assayed with the artificial electron donor reduced methyl viologen (MVH) which transfers electrons directly to the molybdopterin cofactor. These studies have focused on the possible role of protein-bound menaquinone in the structure and function of this multisubunit complex. ^ Nitrate reductase was purified as two distinct forms; after solubilization of membrane proteins with detergents, purification rendered an αβγ complex (holoenzyme) which catalyzes nitrate reduction with MVH or the quinols analogs, menadiol and duroquinol, as electron donors. Alternatively, heat-treatment of the membranes in the absence of detergents and subsequent purification of the active enzyme produced an αβ complex, which reduces nitrate only with MVH as electron donor. The active αβ dimer was also separated from γ subunit by heat treatment of the holoenzyme. ^ Menaquinone-9 was isolated directly from the purified αβ complex, and identified by mass spectrometry. Based on the composition of the membrane quinone pool, it was concluded that menaquinone-9 is sequestered from the membrane pool in a specifically protein-bound form. ^ The role of the bound menaquinone in the structure-function of nitrate reductase was also investigated, along with its participation in UV-light inactivation of the enzyme. Menaquinone-depleted nitrate reductase from a menaquinone deficient mutant retained activity with all electron donors and it remained sensitive to UV inactivation. However, the MVH-nitrate reductase activity and the rate of UV inactivation of the enzyme were significantly reduced and the optical properties of the enzyme were modified by the absence of the bound menaquinone-9. ^ Menaquinone-9 is not absolutely required for electron transfer in nitrate reductase but it appears to be specifically-bound during assembly of the complex and to enhance the transfer of electrons through the complex. The possible plasticity of the functional electron transfer pathway in nitrate reductase is discussed. ^

Correlation between serum total globulins and gamma globulins and their use to diagnose failure of passive transfer in foals.

Various assays have been used as an aid to diagnose failure of passive transfer (FPT) of immunoglobulins in neonatal foals, but often lack sensitivity as screening tests, or are time consuming to perform and impractical as confirmatory tests. The aim of the present study was to evaluate whether measurement of serum total globulins (TG; i.e. total protein minus albumin) can be used to estimate the electrophoretic gamma globulin (EGG) fraction in hospitalised neonatal foals with suspected FPT. Sample data from 56 foals were evaluated retrospectively. The coefficient of rank correlation was 0.84. The area under the curve of ROC analysis was 0.887, 0.922 and 0.930 for EGG concentrations <2 g/L, < 4 g/L and <8 g/L, respectively. Cut-offs for TG achieved ≥90% sensitivity for detecting EGG <2 g/L, < 4 g/L and <8 g/L, with negative predictive values of >97% and >94%, using prevalence of 15% and 30%, respectively. These results suggest that measurement of TG can be used as a guide to predicting EGG, provided that appropriate cut-off values are selected, and this technique could be a useful initial screening test for FPT in foals.

Functional differentiation of spider hemocytes by light and transmission electron microscopy, and MALDI-MS-imaging

The most abundant cell types in the hemolymph of Cupiennius salei are plasmatocytes (70–80%) and granulocytes (20–30%). Both cells differ in shape, cytochemical and transmission electron microscopy staining of their cytoplasma and granules. According to MALDI-IMS (matrix-assisted laser desorption ionization mass spectrometry imaging), granulocytes exhibit ctenidin 1 (9510 Da) and ctenidin 3 (9568 Da), SIBD-1 (8675 Da), and unknown peptides with masses of 2207 and 6239 Da. Plasmatocytes exhibit mainly a mass of 6908 Da. Unknown peptides with masses of 1546 and 1960 Da were detected in plasmatocytes and granulocytes. Transmission electron microscopy confirms the presence of two compounds in one granule and cytochemical staining (light microscopy) tends to support this view. Two further hemocyte types (cyanocytes containing hemocyanin and prehemocytes as stem cells) are only rarely detected in the hemolymph. These four hemocyte types constitute the cellular part of the spider immune system and this is discussed in view of arachnid hemocyte evolution.