Evanescent-wave photoacoustic spectroscopy with optical micro/nano fibers

We demonstrate gas detection based on evanescent-wave photoacoustic (PA) spectroscopy with tapered optical fibers. Evanescent-field instead of open-path absorption is exploited for PA generation, and a quartz tuning fork is used for PA detection. A tapered optical fiber with a diameter down to the wavelength scale demonstrates detection sensitivity similar to an open-path system but with the advantages of easier optical alignment, smaller insertion loss, and multiplexing capability.     

High-sensitivity fiber-tip pressure sensor with graphene diaphragm

A miniature fiber-tip pressure sensor was built by using an extremely thin graphene film as the diaphragm. The graphene also acts as a light reflector, which, in conjunction with the reflection at the fiber end-air interface, forms a low finesse Fabry-Perot interferometer. The graphene based sensor demonstrated pressure sensitivity over 39.4 nm/kPa with a diaphragm diameter of 25 μm. The use of graphene as diaphragm material would allow highly sensitive and compact fiber-tip sensors.     

Option pricing with mean reversion and stochastic volatility

Many underlying assets of option contracts, such as currencies, commodities, energy, temperature and even some stocks, exhibit both mean reversion and stochastic volatility. This paper investigates the valuation of options when the underlying asset follows a mean-reverting lognormal process with stochastic volatility. A closed-form solution is derived for European options by means of Fourier transform. The proposed model allows the option pricing formula to capture both the term structure of futures prices and the market implied volatility smile within a unified framework. A bivariate trinomial lattice approach is introduced to value path-dependent options with the proposed model. Numerical examples using European options, American options and barrier options demonstrate the use of the model and the quality of the numerical scheme.     

Electron‐Deficient Alkynes as Cleavable Reagents for the Modification of Cysteine‐Containing Peptides in Aqueous Medium

Enriched cleavage : An efficient chemoselective cysteine modification of unprotected peptides and proteins has been developed by using electron‐deficient alkynes in aqueous media. Interestingly, terminal alkynone‐modified peptides could be converted back into the unmodified peptides by cleavage by adding thiols under mild conditions (see scheme).

     

Propagation of near-limit gaseous detonations in small diameter tubes

In this study, detonation limits in very small diameter tubes are investigated to further the understanding of the near-limit detonation phenomenon. Three small diameter circular tubes of 1.8, 6.3, and 9.5 mm inner diameters, of 3 m length, were used to permit the near-limit detonations to be observed over long distances of 300 to 1500 tube diameters. Mixtures with high argon dilution (stable) and without dilution (unstable) are used for the experiments. For stable mixtures highly diluted with argon for which instabilities are not important and where failure is due to losses only, the limit obtained experimentally appears well to be in good agreement in comparison to that computed by the quasi-steady ZND theory with flow divergence or curvature term modeling the boundary layer effects. For unstable detonations it is suggested that suppression of the instabilities of the cellular detonation due to boundary conditions is responsible for the failure of the detonation wave. Different near-limit propagation regimes are also observed, including the spinning and galloping mode. Based on the present experimental results, an attempt is made to study an operational criterion for the propagation limits of stable and unstable detonations.     

Synthesis and optical properties of hyperbranched polyarylenes and linear polyacetylenes

New hyperbranched polyarylenes (HPAs) and linear polyacetylenes (LPAs) containing chromophoric moieties were synthesized in high yields (up to 97%) by coablt- and tantalum-catalyzed polycyclotrimerizations and tungsten-catalyzed metathesis polymerizations, respectively. The polymers possessed high molecular weights (M_w up to 113 000 Da) and were completely soluble in common organic solvents. The HPAs emitted strong UV light of 400 nm in high quantum yields (Φ_F up to 0.98) and limited intense laser pulses, whose limiting threshold and signal suppress power were better than those of C₆₀, a well-known optical limiter. The electroluminescence (EL) devices of the LPAs emitted blue light of ∼460 nm and exhibited maximun brightness, current efficiency, and external quantum efficiency of 1118 cd/m², 1.53 cd/A, and 0.85%, respectively.     

Synthesis,Structure, and Spectroscopic and Electrochemical Properties of Heteroleptic Bis(phthalocyaninato) Rare Earth Complexes with a C4 Symmetry

A series of eleven heteroleptic bis(phthalocyaninato) rare earth double‐deckers [M^III(pc){pc(α‐OC₅H₁₁)₄}] 1 – 11 (M=Y, Sm? Lu; pc=phthalocyaninato; pc(α‐OC₅H₁₁)₄=1,8,15,22‐tetrakis(1‐ethylpropoxy)phthalocyaninato) were prepared as racemic mixtures by [M^III(pc)(acac)]‐induced (acac=acetylacetonato) cyclic tetramerization of 3‐(1‐ethylpropoxy)phthalonitrile in the presence of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) in refluxing pentanol. These compounds could also be prepared by treating [M^III(pc)(acac)] with the metal‐free phthalocyanine H₂{pc(α‐OC₅H₁₁)₄} in refluxing octanol. The whole series of double‐decker complexes 1 – 11 were characterized by elemental analysis and various spectroscopic methods. The molecular structures of the Sm, Eu, and Er complexes 1, 2 , and 8 , respectively, were also determined by single‐crystal X‐ray diffraction analysis. The effects of the rare earth ion size on the reaction yield, molecular structure, and spectroscopic and electrochemical properties of these complexes were systematically examined.     

A theoretical study of potassium cation binding to glycylglycine (GG) and alanylalanine (AA) dipeptides

By combining Monte Carlo conformational search technique with high-level density functional calculations, the geometry and energetics of K(+) interaction with glycylglycine (GG) and alanylalanine (AA) were obtained for the first time. The most stable K(+)-GG and K(+)-AA complexes are in the charge-solvated (CS) form with K(+) bound to the carbonyl oxygens of the peptide backbone, and the estimated 0 K binding affinities (DeltaH(0)) are 152 and 157 kJ mol(-1), respectively. The K(+) ion is in close alignment with the molecular dipole moment vector of the bound ligand, that is, electrostatic ion-dipole interaction is the key stabilizing factor in these complexes. Furthermore, the strong ion-dipole interaction between K(+) and the amide carbonyl oxygen atom of the peptide bond is important in determining the relative stabilities of different CS binding modes. The most stable zwitterionic (ZW) complex involves protonation at the amide carbonyl oxygen atom and is approximately 48 kJ mol(-1) less stable than the most stable CS form. The usefulness of proton affinity (PA) as a criterion for estimating the relative stability of ZW versus CS binding modes is examined. The effect of chain length and the nature of metal cations on cation-dipeptide interactions are discussed. Based on results of this study, the interaction of K(+) with longer peptides consisting of aliphatic amino acids are rationalized.     

Two-dimensional infrared spectroscopy of antiparallel beta-sheet secondary structure

We investigate the sensitivity of femtosecond Fourier transform two-dimensional infrared spectroscopy to protein secondary structure with a study of antiparallel beta-sheets. The results show that 2D IR spectroscopy is more sensitive to structural differences between proteins than traditional infrared spectroscopy, providing an observable that allows comparison to quantitative models of protein vibrational spectroscopy. 2D IR correlation spectra of the amide I region of poly-l-lysine, concanavalin A, ribonuclease A, and lysozyme show cross-peaks between the IR-active transitions that are characteristic of amide I couplings for polypeptides in antiparallel hydrogen-bonding registry. For poly-l-lysine, the 2D IR spectrum contains the eight-peak structure expected for two dominant vibrations of an extended, ordered antiparallel beta-sheet. In the proteins with antiparallel beta-sheets, interference effects between the diagonal and cross-peaks arising from the sheets, combined with diagonally elongated resonances from additional amide transitions, lead to a characteristic "Z"-shaped pattern for the amide I region in the 2D IR spectrum. We discuss in detail how the number of strands in the sheet, the local configurational disorder in the sheet, the delocalization of the vibrational excitation, and the angle between transition dipole moments affect the position, splitting, amplitude, and line shape of the cross-peaks and diagonal peaks.