The single-mode rate equations for semiconductor lasers with thermal effects

A mathematical model describing the coupling of electrical,optical and thermal effects in semiconductor lasers is introduced.Numerical and asymptotic solutions are derived, including expressionsfor key physical quantities such as the initial time delay,the frequency of spike oscillation and the temperature rise,together with its influence on the photon density, the electronconcentration and the threshold current. The consequences ofthermal effects in reducing efficiency are thus quantified.     

Cranking an SU(3)-symmetric chiral soliton

The chiral quark—meson model based on a linear σ model is extended to three flavours of quarks. For an SU(3)-symmetric version of the model we use a lowest-order cranking approach to calculate the splittings between the baryon multiplets. The isospin cranking which governs the octet—decuplet splitting is identical to that in the SU(2) model. The moment of inertia for “strange” rotations gives the energies of states which must involve mesonic excitations. It is found to be small, indicating that such states, if they exist, lie well above the nucleon.     

Microscale Crystals of Cytochrome c and Calixarene on Electrodes: Interprotein Electron Transfer between Defined Sites

The assembly of redox proteins on electrodes is an important step in biosensor development. Recently, p‐sulfonato‐calix[4]arene was shown to act as “molecular glue” for the assembly and crystallization of cytochrome c (cyt c). Electrochemical data are presented for microscale cyt c–calixarene crystals grown on self‐assembled monolayers (SAM)‐modified Au electrodes. The crystals were characterized by cyclic voltammetry and exceptionally high concentrations of electroactive cyt c were obtained. The peak currents were found to increase linearly with the square root of the scan rate, thus allowing an evaluation of the rate constant for electron self‐exchange. This study revealed high electroactivity accompanied by fast interprotein electron transfer in crystals, which may have implications for the construction of novel bioelectronic devices.     

Novel copolymers of styrene. 11. Fluoro ring-substituted butyl 2-cyano-3-phenyl-2-propenoates

Novel trisubstituted ethylenes, fluorine ring-substituted butyl 2-cyano-3-phenyl-2-propenoates, RPhCHC?(CN)CO₂C₄H₉ (where R is 2,3-diF, 2,4-diF, 2,5-diF, 2,6-diF, 3,4-diF, 3,5-diF, and 2,4,5-triF) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-substituted benzaldehydes and butyl cyanoacetate, and characterized by CHN analysis, IR, ¹H and ¹³C-NMR. All the ethylenes were copolymerized with styrene (M₁) in solution with radical initiation (ABCN) at 70°C. The compositions of the copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, ¹H and ¹³C-NMR. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200-500°C range with residue (1.5–2.3% wt.), which then decomposed in the 500–800°C range.     

Electronic and optical properties of magnesium phthalocyanine (MgPc) solid films studied by soft X-ray excited optical luminescence and X-ray absorption spectroscopies

In a study to link the optical and structural properties of solid films of magnesium Phthalocyanine (MgPc), a range of synchrotron based spectroscopic methods have been used. These include X-ray excited optical luminescence (XEOL) together with X-ray absorption spectroscopy (XAS) measured both by total electron yield methods (TEY) and by using the optically detected photoluminescence yield method (PLY). XEOL spectra below K shell threshold show a broad emission peak at approximately 860 nm which can be attributed to the optical Q-band of these organic systems, which is then suppressed above the threshold. The shift to higher wavelength compared to optical emission spectra from MgPc in solution is consistent with intermolecular coupling of the excited states in the loosely intermolecular bonded phthalocyanine crystal structure. Zero order total PLY spectra at both C and N K edges are compared to TEY spectra where at the C K edge an inversion of intensity ratios between features is observed. Wavelength-specific PLY absorption spectra taken at 860 nm at the N K edge show a role for sigma* states participating in the luminescence process possibly through the sigma-like lone pair of bridging nitrogen atom, denoted the n --> pi* transition.     

Label-free flow-enhanced specific detection of Bacillus anthracis using a piezoelectric microcantilever sensor

Differentiation between species of similar biological structure is of critical importance in biosensing applications. Here, we report specific detection of Bacillus anthracis (BA) spores from that of close relatives, such as B. thuringiensis (BT), B. cereus (BC), and B. subtilis (BS) by varying the flow speed of the sampling liquid over the surface of a piezoelectric microcantilever sensor (PEMS). Spore binding to the anti-BA spore IgG coated PEMS surface is determined by monitoring the resonance frequency change in the sensor's impedance vs. frequency spectrum. Flow increases the resonance frequency shift at lower flow rates until the impingement force from the flow overcomes the binding strength of the antigen and decreases the resonance frequency shift at higher flow rates. We showed that the change from increasing to decreasing resonance frequency shift occurred at a lower fluid flow speed for BT, BC, and BS spores than for BA spores. This trend reduces the cross reactivity ratio of BC, BS, and BT to the anti-BA spore IgG immobilized PEMS from around 0.4 at low flow velocities to less than 0.05 at 3.8 mm s(-1). This cross reactivity ratio of 0.05 was essentially negligible considering the experimental uncertainty. The use of the same flow that is used for detection to further distinguish the specific binding (BA to anti-BA spore antibody) from nonspecific binding (BT, BC, and BS to anti-BA spore antibody) is unique and has great potential in the detection of general biological species.     

Picosecond infrared probing of the vibrational spectra of transients formed upon UV excitation of stacked G-tetrad structures

The photophysical properties of stacked G-tetrads in diverse systems, including concentrated solutions of 5'-guanosine monophosphate (5'-GMP), polyguanylic acid (poly(G)) and the G-rich oligodeoxynucleotide sequence characteristic of human telomeric DNA, are probed by ps-TRIR and compared to those of the monomeric 5'-GMP.     

A generalization of the Jaffard–Ohm–Kaplansky Theorem

The well-known Jaffard–Ohm–Kaplansky Theorem states that every abelian ?-group can be realized as the group of divisibility of a commutative Bézout domain. To date there is no realization (except in certain circumstances) of an arbitrary, not necessarily abelian, ?-group as the group of divisibility of an integral domain. We show that using filters on lattices we can construct a nice quantal frame whose “group of divisibility” is the given ?-group. We then show that our construction when applied to an abelian ?-group gives rise to the lattice of ideals of any Prüfer domain assured by the Jaffard–Ohm–Kaplansky Theorem. Thus, we are assured of the appropriate generalization of the Jaffard–Ohm–Kaplansky Theorem.     

Surface structure effects via photoexcited core electron diffraction for Na on Ni

Photoemission from the Na 2p core level has been measured in the range ?ω = 40–120 eV for a c(2×2) Na overlayer on a Ni(001). surface. Weak oscillations in the Na 2p emission intensity vs. wavelength were observed and are interpreted as due to photoelectron scattering. The observed peaks closely match, in energy, those derived in recent calculations which assume the Na occupies a hollow site 2.23Å above the Ni surface layer. The data therefore indicate that observation and calculation of such effects may allow surface structure determinations.