Bacterial bioluminescence, bioelectromagnetics and function

The biological functions of light emission in bacterial bioluminescence are not always obvious, especially if the bacteria are in a free-living mode. Experimental evidence suggests that light emission confers benefit to the bacteria themselves such as through photoreactivation and involves as much as 20% of cell energy metabolism. A theoretical model shows if the effect is mediated solely by light then cells should be luminescent at both high and low cell densities, therefore raising doubt over the photoreactivation hypothesis and suggesting that another cofactor is involved. It has been postulated that bioelectromagnetics may be involved in biological processes and be involved with coordinated activity in quorate cells. The cell densities associated with autoinduction coincide with a large change in coupling efficiency in the millimeter and submillimeter spectral region. In this paper it is suggested that one function of bioluminescence is as a pump, involving millimeter and submillimeter wave coupling that is of benefit to the quorum. This may be related to the observation that millimeter wave radiation exposure has been reported to induce changes in DNA conformation and possibly gene expression. Agents that change DNA conformation in bioluminescent bacteria can cause increases in light emission. This work may have implications for electromagnetic fields as quorum-quenching agents.     

Liquid crystal birefringence for millimeter wave radar

Abstract

Many liquid crystals are found to have relatively high birefringence (Δn) values in the microwave and millimeter wave regions, as calculated from the phase shift induced by their reorientation by magnetic or electric fields. At 30 GHz, Δn values were obtained in the range of 0.08 to 0.18 for eleven liquid crystal mixtures of various types. The most favourable liquid crystal structures for high millimeter wave birefringence are highly conjugated rod-like molecules containing biphenyl, terphenyl, phenylpyrimidine, biphenylpyrimidine, and tolane groups in nematics of positive dielectric anisotropy (Δε). However, other liquid crystal structures including Schiffs base, azoxybenzene, and aromatic ester groups also have substantial birefringence, including nematics with negative and crossover Δε, as well as cholesteric nematics. The Δn varied only slightly at different frequencies of microwave millimeter wave in the 15–94 GHz range. Studies on magnetic and electrical field liquid crystal orientation in specially designed waveguides provide a basis for new types of modulators and scanning array antennae in the millimeter wave region, where more compact liquid crystal modulation media can be used than in the microwave region. These scanners can be used for both sending and receiving radar signals for potentially low cost radar systems.     

The rotational spectrum and structure of HOOOH

Dihydrogen trioxide, HOOOH, which is a species with fundamental importance for understanding the chain formation ability of the oxygen atom, was detected in a supersonic jet by a Fourier transform microwave spectrometer with a pulsed discharge nozzle, together with double resonance and triple resonance techniques. Its precise molecular structure was determined from the experimentally determined rotational constants of HOOOH and its isotopomer, DOOOD. Many of the microwave and millimeter wave transitions can now be accurately predicted, which could be facilitated for remote sensing of the molecule to elucidate its roles in various chemical processes.     

钡铁氧体包覆碳纤维的制备及毫米波衰减性能

通过溶胶凝胶法,在碳纤维表面均匀包覆了一层厚度约为1 μm的钡铁氧体(BaFe₁₂O₁₉)。采用SEM、FTIR、XRD、XPS等技术对碳纤维/钡铁氧体复合材料的组成、结构、性能进行了表征和分析。利用8 mm波雷达装置测试了碳纤维、碳纤维/钡铁氧体复合材料的毫米波衰减性能。实验结果表明：由于碳纤维/钡铁氧体复合材料兼具电损耗和磁损耗吸收,其8 mm波衰减性能明显优于单纯的碳纤维。     

Dynamics of small,floppy molecules studied by high-resolution spectroscopic techniques

In molecular spectroscopy one of the common interests is how to transform the information obtained by high-resolution spectroscopic techniques into some reliable approximation of the potential energy surface of a particular molecule. Traditionally vibrational spectroscopy has been used. Rotational spectroscopy can only probe, at least at room temperature, molecular transitions arising from excited vibrational states up to approximately 1000 cm^?1. This corresponds roughly to 10% of a typical bond dissociation energy. However, floppy molecules which exhibit a large-amplitude, low-lying vibrational mode can be studied to a large extent by rotational spectroscopy in the microwave, millimeter and submillimeter wave range. Quasilinearity is a special form of large-amplitude motion, which complicates the observed molecular spectra substantially and which presents a real challenge to theoretical spectroscopists. In this lecture the highlights of quasilinear behavior of the molecules HCNO, OCCCO, HNCS and HNCO will be discussed. Another form of large amplitude motion is the inversion exhibited primarily by molecules derived from NH₃. Isocyanamide will be discussed and its special spectroscopic features will be shown. Cyanamide and isocyanamide are potential prebiotic molecules: cyanamide has been detected as a constituent in the interstellar medium. The analysis of the molecular dynamics of these molecules is shown to be necessary for understanding the frequencies and intensities of the observed spectra in the laboratory and in interstellar space.     

Weak, improper, C-O...H-C hydrogen bonds in the dimethyl ether dimer

The ground-state rotational spectrum of the dimethyl ether dimer, (DME)(2), has been studied by molecular beam Fourier transform microwave and free jet millimeter wave absorption spectroscopies. The molecular beam Fourier transform microwave spectra of the (DME-d(6))(2), (DME-(13)C)(2), (DME-d(6))...(DME), (DME-(13)C)...(DME), and (DME)...(DME-(13)C) isotopomers have also been assigned. The rotational parameters have been interpreted in terms of a C(s) geometry with the two monomers bound by three weak C-H...O hydrogen bonds, each with an average interaction energy of about 1.9 kJ/mol. The experimental data combined with high-level ab initio calculations show this kind of interaction to be improper, blue-shifted hydrogen bonding, with an average shortening of the C-H bonds involved in the hydrogen bonding of 0.0014 A. The length of the C-H...O hydrogen bonds, r(O...H), is in the range 2.52-2.59 A.     

石墨烯掺杂碳气凝胶粉体的制备及电磁干扰性能

采用溶胶-凝胶、 超临界干燥及高温裂解技术制备了不同石墨烯掺杂量的碳气凝胶(G-CA)粉体材料, 通过控制材料的组成和微观结构, 制备了密度仅为0.0093 g/cm³的低密度高导电性气凝胶粉体. 将G-CA粉体布撒在空气中, 测试其对毫米波、 可见光和红外光的衰减性能. 结果表明, 相对于纯碳气凝胶和纯石墨烯气凝胶, G-CA粉体对3种波段的电磁波的衰减性能大幅度提高. 其中石墨烯/掺杂量为7%的碳气凝胶(7%G-CA)在布撒初期和布撒20 min后, 对红外光和可见光均具有97%和94%以上的遮蔽率; 对于毫米波, 在布撒初期和布撒10 min以后, 分别具有75%和65%以上的遮蔽率. G-CA粉体具有良好的分等级微纳米结构及高导电性和超低密度, 该微观结构与组成的协同作用使其呈现出优异的多波段、 长时有效的电磁干扰性能, 有望扩展和延伸传统烟幕材料的应用范围.     

Fourier transform microwave and millimeter wave spectroscopy of quinazoline, quinoxaline, and phthalazine

The pure rotational spectra of the bicyclic aromatic nitrogen heterocycle molecules, quinazoline, quinoxaline, and phthalazine, have been recorded and assigned in the region 13-87 GHz. An analysis, guided by ab initio molecular orbital predictions, of frequency-scanned Stark modulated, jet-cooled millimeter wave absorption spectra (48-87 GHz) yielded a preliminary set of rotational and centrifugal distortion constants. Subsequent spectral analysis at higher resolution was carried out with Fourier transform microwave (FT-MW) spectroscopy (13-18 GHz) of a supersonic rotationally cold molecular beam. The high spectral resolution of the FT-MW instrument provided an improved set of rotational and centrifugal distortion constants together with nitrogen quadrupole coupling constants for all three species. Density functional theory calculations at the B3LYP∕6-311+G?? level of theory closely predict rotational constants and are useful in predicting quadrupole coupling constants and dipole moments for such species.     

Millimeter-wave-detected, millimeter-wave optical polarization spectroscopy

We report a new form of microwave optical double-resonance spectroscopy called millimeter-wave-detected, millimeter-wave optical polarization spectroscopy (mmOPS). In contrast to other forms of polarization spectroscopy, in which the polarization rotation of optical beams is detected, the mmOPS technique is based on the polarization rotation of millimeter waves induced by the anisotropy from optical pumping out of the lower or upper levels of the millimeter wave transition. By monitoring ground-state rotational transitions with the millimeter waves, the mmOPS technique is capable of identifying weak or otherwise difficult-to-observe optical transitions in complex chemical environments, where multiple molecular species or vibrational states can lead to spectral congestion. Once a transition is identified, mmOPS can then be used to record pure rotational transitions in vibrationally and electronically excited states, with the resolution limited only by the radiative decay rate. Here, the sensitivity of this nearly-background-free technique is demonstrated by optically pumping the weak, nominally spin-forbidden CS e (3)Sigma(-)-X (1)Sigma(+) (2-0) and d (3)Delta-X (1)Sigma(+) (6-0) electronic transitions while probing the CS X (1)Sigma(+) (v(")=0,J(")=2-1) rotational transition with millimeter waves. The J(')=2,N(')=2<--J(')=1,N(')=1 pure rotational transition of the CS e (3)Sigma(-) (v(')=2) state is then recorded by optically preparing the J(')=1,N(')=1 level of the e (3)Sigma(-) (v(')=2) state via the J(')=1,N(')=1<--J(")=1 transition of the e (3)Sigma(-)-X (1)Sigma(+) (2-0) band.     

Equatorial and axial hydrogens in heterocyclic six-membered rings: the rotational spectrum of piperazine

The rotational spectrum of piperazine has been investigated by free jet absorption millimeter wave spectroscopy. The spectrum of the polar conformer with axial–equatorial orientations of the two amino hydrogens was only observed. This assignment was confirmed by the spectra of the two monodeuterated and the bideuterated species.Ab initio and density functional calculations predict the observed conformer to have an energy intermediate between the equatorial–equatorial and axial–axial non-polar forms, the former species being the global minimum.     

Organic Photomechanical Materials

Organic molecules can transform photons into Angstrom‐scale motions by undergoing photochemical reactions. Ordered media, for example, liquid crystals or molecular crystals, can align these molecular‐scale motions to produce motion on much larger (micron to millimeter) length scales. In this Review, we describe the basic principles that underlie organic photomechanical materials, starting with a brief survey of molecular photochromic systems that have been used as elements of photomechanical materials. We then describe various options for incorporating these active elements into a solid‐state material, including dispersal in a polymer matrix, covalent attachment to a polymer chain, or self‐assembly into molecular crystals. Particular emphasis is placed on ordered media, such as liquid‐crystal elastomers and molecular crystals, that have been shown to produce motion on large (micron to millimeter) length scales. We also discuss other mechanisms for generating photomechanical motion that do not involve photochemical reactions, such as photothermal expansion and photoinduced charge transfer. Finally, we identify areas for future research, ranging from the study of basic phenomena in solid‐state photochemistry, to molecular and host matrix design, and the optimization of photoexcitation conditions. The ultimate realization of photon‐fueled micromachines will likely involve advances spanning the disciplines of chemistry, physics and engineering.     

利用嵌段共聚物及无机盐合成高质量的立方相、大孔径介孔氧化硅球

使用非离子型嵌段高分子表面活性剂为模板剂,在无机盐的作用下,合成了直 径在2～4 mm、高度有序、立方相的介孔氧化硅SBA-16球。利用无机盐来调变无机 /有机物种之间的作用力和自组装能力,不仅在介观尺寸上提高了所合成介孔材料 的有序程度,而且在宏观上控制了介孔材料的形貌。经焙烧后的SBA-16球材料比表 面积为750 m~2/g,孔容为0.52 cm~3/g,孔径为7.8 nm。具有大孔径的SBA-16球材 料可以更方便地应用于大分子吸附和分离等领域。     

Shear-flow-based chromatographic separations as an alternative to pressure-driven liquid chromatography

It is only by developing specially designed injection and detection systems that shear-driven chromatography can become a viable alternative to HPLC. In the present paper, a dedicated zero dead-volume injection procedure is presented with which sample volumes can be injected reproducibly in the required picoliter range. In addition, a transversal detection groove system is designed which should allow to perform on-line UV-VIS absorption measurements with path lengths in the millimeter range, with an acceptable theoretical plate loss (only 20% in a 5 cm long channel) and acting as a nearly perfect wave guide.     

Plane wave/pseudopotential implementation of excited state gradients in density functional linear response theory: a new route via implicit differentiation

This work presents the formalism and implementation of excited state nuclear forces within density functional linear response theory using a plane wave basis set. An implicit differentiation technique is developed for computing nonadiabatic coupling between Kohn-Sham molecular orbital wave functions as well as gradients of orbital energies which are then used to calculate excited state nuclear forces. The algorithm has been implemented in a plane wave/pseudopotential code taking into account only a reduced active subspace of molecular orbitals. It is demonstrated for the H(2) and N(2) molecules that the analytical gradients rapidly converge to the exact forces when the active subspace of molecular orbitals approaches completeness.     

Thermally Driven Polymorphic Transition Prompting a Naked‐Eye‐Detectable Bending and Straightening Motion of Single Crystals

The amplification of molecular motions so that they can be detected by the naked eye (10⁷‐fold amplification from the ångström to the millimeter scale) is a challenging issue in the development of mechanical molecular devices. In this context, the perfectly ordered molecular alignment of the crystalline phase has advantages, as demonstrated by the macroscale mechanical motions of single crystals upon the photochemical transformation of molecules. In the course of our studies on thermoresponsive amphiphiles containing tetra(ethylene glycol) (TEG) moieties, we serendipitously found that thermal conformational changes of TEG units trigger a single‐crystal‐to‐single‐crystal polymorphic phase transition. The single crystal of the amphiphile undergoes bending and straightening motion during both heating and cooling processes at the phase‐transition temperatures. Thus, the thermally triggered conformational change of PEG units may have the advantage of inducing mechanical motion in bulk materials.     

Polarons in one‐dimensional molecular chains with intermolecular and intramolecular vibrations

Polarons are investigated in a model for one‐dimensional molecular chains involving both acoustical and optical lattice vibrations, as found in diatomic chains. With the help of a specific ansatz for low‐lying quasiparticles, a continuum limit approximation sustains the existence of analytical solutions to the model. The dispersion energy as well as the effective mass of low‐lying electronic states in the presence of the two lattice mode‐induced polaronic quasiparticle, are derived analytically. It is found that the band effective mass is strongly enhanced by a factor depending on the two electron–lattice coupling constants. A test of stability of the analytical shapes of the three long‐wavelength excitations is carried out numerically by following their simultaneous propagation throughout the molecular lattice. The long‐wavelength polaron appears to be very stable within an acceptable range of values of the electron wave vector and propagates faster and faster as one moves from the groundstate toward mid‐band states. However, the accompanying kink and pulse soliton deformations are always slower consistently with the adiabatic considerations underlying the quasi‐classical treatment followed in this work. In addition, the kink component of the lattice deformation tends to become unstable at relatively large electronic wave vectors, while the polaron and in turn the optical lattice deformation are more and more stable, traducing dominant optical modes of the lattice in the process of formation of polaron. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Spectroscopic Characterization of a Steam Arc Cutting Torch

Optical emission spectroscopy has been used to investigate the characteristics of a plasma jet produced by a steam arc cutting torch operated in air at atmospheric pressure. A procedure has been developed for simultaneous determination of temperature and pressure in the plasma jet as well as an effective nonequilibrium factor. It is based on comparison of a few experimental and simulated spectral quantities. The experimental data were obtained from the spectrum of H_β and OII lines centred at 480 nm. The existence of the shock wave structure characteristic of an underexpanded jet can clearly be deduced from the measured properties. In the first expansion region, the centreline pressure drops from about 1.4 atm at the nozzle exit to about 0.7 atm a few tenths of millimeter downstream. On the contrary, the centreline temperature remains almost unchanged within this region and reaches the value of about 23,000 K.     

Competition between metal-amido and metal-imido chemistries in the alkaline earth series: an experimental and theoretical study of BaNH

The pure rotational spectrum of BaNH in its X(1)Sigma(+) ground electronic state has been recorded using millimeter/submillimeter direct absorption methods; data for the deuterium and barium 137 isotopomers have been measured as well. The molecules were produced by the reaction of ammonia or ND(3) and barium vapor in the presence of a dc discharge. Transitions arising from the ground vibrational state and the excited vibrational bending (01(1)0) and heavy atom stretching (100) modes were measured. The rotational spectrum indicates a linear structure, with B(0)(BaNH) = 7984.549 MHz and B(0)(BaND) = 7060.446 MHz. An r(m)((1)) structure has been determined, yielding r(BaN) = 2.077 +/- 0.002 Angstroms and r(NH) = 1.0116 +/- 0.0006 Angstroms. Density functional calculations using an extensive Slater-type basis set with inclusion of scalar relativistic effects gives geometrical parameters and vibrational frequencies for BaNH in excellent agreement with those determined by experiment. The molecular orbital and natural bond order analyses of the BaNH wave function show Ba-N pi bonds formed by electron donation from the formally filled N 2p orbitals of the imido group to the empty Ba 5d orbitals. The multiple bonding between Ba and N stabilizes the linear geometry and, along with the relative ease of oxidation of the Ba atom, favors formation of the metal-imido species over that of the metal-amido species that have been found from similar studies with Mg, Ca, and Sr atoms in this group.