Reinvestigation of the ν2 + 2ν3 subband in the overtone icosad of 12CH4 using cavity ring-down (CRD) spectroscopy of a supersonic jet expansion

We report a detailed reinvestigation of the ν₂?+?2ν₃ combination band of methane ¹²CH₄ centred at (7510.3378?±?0.003)?cm^?1 ((225.154263?±?0.0001)?THz) within the icosad of the overtone absorption. A new experimental setup is described, allowing us to carry out cw-laser cavity ring-down spectroscopy (cw-CRDS) at instrumental resolution in the MHz range in seeded supersonic jet expansions down to rotational temperature of 7?K compared to previous cw-CRDS measurements in our group achieving about 50?K in expansions of neat CH₄. We provide a careful re-analysis on the basis of our new experimental results for the Q and R branch transitions including data obtained between about 7 and 300?K under various conditions. We resolve previously observed discrepancies of assignments and are able to present a definitive assignment for lines involving angular momentum quantum numbers up to J?=?4. The analysis of relative intensities in spectra taken at rotational and effective translational temperatures between about 50?K and less than 10?K indicate conservation of nuclear spin symmetry upon supersonic jet expansion, in agreement with previous results using other techniques and covering other spectral ranges.     

In vitro monitoring of goat-blood glycemia with a microwave biosensor

We used an electromagnetic microwave cavity sensor for real time measurement of the glycemia in goat-blood for three animals. We could determine the concentration of d-glucose in blood in the range of 90–550 mg/dl at the resonance frequency near 4.76 GHz with a bandwidth of 300 MHz. The change in microwave reflection coefficient S₁₁ (due to the variation of d-glucose concentration in blood) was about 16.33 dB, 23.92 dB, 7.66 dB and resonance frequency shift was about 21.78 MHz, 36.29 MHz, 20.77 MHz, respectively, for the three different samples. The in vitro results show the measured signal-to-noise ratio of about 32 dB, and the minimum detectable signal level of about 0.025 dB/(mg/dl). The results clearly show the sensitivity and usefulness of this microwave sensor for these types of biological investigations. This proposed system provides a unique approach for real contactless glucose monitoring and, it may serve as a bloodless glucometer for the calibration of different glucose levels.     

The structure factor for liquid lead

Abstract

The structure factor for liquid lead at the temperatures 613 K, 643 K, 863 K and 1163 K are measured by neutron diffraction. Extensive comparisons to earlier measurements are made as well as comparisons to different hard-core models.     

Non-Poissonian statistics in an optical analog of quantum billiard with perfectly square boundaries

We study deviation from the Poissonian statistics of the frequency spacing distribution, appearing due to coupling of polarizational and transverse degrees of freedom in a perfectly square vertical cavity surface emitting laser. The deviation can be controlled by strength of the intracavity anisotropy and its alignment to the device boundaries.     

Generation of sub‐terahertz repetition rates from a monolithic self‐mode‐locked laser coupled with an external Fabry‐Perot cavity

A novel scheme to multiply the repetition rate of a monolithic self‐mode‐locked laser for generating sub‐terahertz pulse sources is successfully demonstrated. A coated Yb:KGW crystal is designed to achieve a self‐mode‐locked operation at a repetition rate of 24 GHz with an average output power exceeding 1.0 W at a pump power of 4.8 W. A partially reflective mirror is utilized to combine with the output surface of the gain medium to constitute an external Fabry‐Perot cavity. It is theoretically and experimentally verified that adjusting the external cavity length to satisfy the commensurate condition can lead to the frequency spacing to be various order harmonics of the mode spacing of the monolithic cavity. The maximum pulse repetition rate of the laser output can be up to 216 GHz and the pulse duration is as short as 330 fs. More importantly, the overall characteristics of the first‐order temporal autocorrelation traces obtained by sequentially scanning the external cavity.length display an intriguing phenomenon of temporally fractional revivals, similar to the feature of spatial Talbot revivals.

     

Gelation Kinetics-Structure Analysis of pH-triggered Low Molecular Weight Hydrogelators

Properties such as shear modulus, gelation time, structure of supramolecular hydrogels are strongly dependent on self-assembly, gelation triggering mechanism and processes used to form the gel. In our work we extend reported rheology analysis methodologies to pH-triggered supramolecular gels to understand structural insight using a model system based on N−N’ Dibenzoyl-L-Cystine pH-triggered hydrogelator and Glucono-δ-Lactone as the trigger. We observed that Avrami growth model when applied to time-sweep rheological data of gels formed at lower trigger concentrations provide estimates of fractal dimension which agree well compared with visualization of the microstructure as seen via Confocal Laser Scanning Microscopy, for a range of gelator concentrations.     

Spatially Resolved Confocal Resonant Raman Microscopic Analysis of Anode‐Grown Geobacter sulfurreducens Biofilms

When grown on the surface of an anode electrode, Geobacter sulfurreducens forms a multi‐cell thick biofilm in which all cells appear to couple the oxidation of acetate with electron transport to the anode, which serves as the terminal metabolic electron acceptor. Just how electrons are transported through such a biofilm from cells to the underlying anode surface over distances that can exceed 20 microns remains unresolved. Current evidence suggests it may occur by electron hopping through a proposed network of redox cofactors composed of immobile outer membrane and/or extracellular multi‐heme c‐type cytochromes. In the present work, we perform a spatially resolved confocal resonant Raman (CRR) microscopic analysis to investigate anode‐grown Geobacter biofilms. The results confirm the presence of an intra‐biofilm redox gradient whereby the probability that a heme is in the reduced state increases with increasing distance from the anode surface. Such a gradient is required to drive electron transport toward the anode surface by electron hopping via cytochromes. The results also indicate that at open circuit, when electrons are expected to accumulate in redox cofactors involved in electron transport due to the inability of the anode to accept electrons, nearly all c‐type cytochrome hemes detected in the biofilm are oxidized. The same outcome occurs when a comparable potential to that measured at open circuit (?0.30 V vs. SHE) is applied to the anode, whereas nearly all hemes are reduced when an exceedingly negative potential (?0.50 V vs. SHE) is applied to the anode. These results suggest that nearly all c‐type cytochrome hemes detected in the biofilm can be electrochemically accessed by the electrode, but most have oxidation potentials too negative to transport electrons originating from acetate metabolism. The results also reveal a lateral heterogeneity (x–y dimensions) in the type of c‐type cytochromes within the biofilm that may affect electron transport to the electrode.