Single-fiber diffuse optical time-of-flight spectroscopy

We demonstrate interstitial diffuse optical time-of-fight spectroscopy based on a single fiber for both light delivery and detection. Detector saturation due to the massive short-time reflection is avoided by ultrafast gating of a single photon avalanche diode. We show that the effects of scattering and absorption are separable and that absorption can be assessed independently of scattering. Measurements on calibrated liquid phantoms and subsequent Monte Carlo-based evaluation illustrate that absorption coefficients can be accurately assessed over a wide range of medically relevant optical properties. Our findings pave the way to simplified and less invasive interstitial in vivo spectroscopy.     

Experimental demonstration of subcarrier multiplexed quantum key distribution system

We provide, to our knowledge, the first experimental demonstration of the feasibility of sending several parallel keys by exploiting the technique of subcarrier multiplexing (SCM) widely employed in microwave photonics. This approach brings several advantages such as high spectral efficiency compatible with the actual secure key rates, the sharing of the optical fainted pulse by all the quantum multiplexed channels reducing the system complexity, and the possibility of upgrading with wavelength division multiplexing in a two-tier scheme, to increase the number of parallel keys. Two independent quantum SCM channels featuring a sifted key rate of 10 Kb/s/channel over a link with quantum bit error rate <2% is reported.     

Ultrafast molecular rotor: an efficient sensor for premelting of natural DNA

Structural changes in nucleic acids in the premelting region (T < melting temperature, T(m)) play an important role in the biological activity of DNA at physiological temperature. In the present communication we report the use of an ultrafast molecular rotor as an extrinsic fluorescence sensor to monitor the structural changes in natural DNA at T < T(m), which could not be detected even by circular dichroism spectroscopy. Further, the fluorescence sensor used in the present study is superior than most commonly used DNA stains.     

Theoretical study of methoxy group influence in the gas‐phase elimination kinetics of methoxyalkyl chlorides

The unimolecular gas‐phase elimination kinetics of 2‐methoxy‐1‐chloroethane, 3‐methoxy‐1‐chloropropane, and 4‐methoxyl‐1‐chloroburane has been studied by using density functional theory (DFT) methods to propose the most reasonable mechanisms of decomposition of the aforementioned compounds. Calculation results of 2‐methoxy‐1‐chloroethane and 3‐methoxy‐1‐chloropropane suggest dehydrochlorination through a concerted nonsynchronous four‐centered cyclic transition state (TS) to give the corresponding olefin. In the case of 4‐methoxyl‐1‐chloroburane, in addition to the 1,2‐elimination mechanism, the anchimeric assistance by the methoxy group, through a polar five‐centered cyclic TS, provides additional pathways to give 4‐methoxy‐butene, tetrahydrofuran and chloromethane. The bond polarization of the C? Cl, in the direction of C^δ+ ··· Cl^δ?, is the limiting step of these elimination reactions. The significant increase in rate together with the formation of a cyclic product tetrahydrofuran in the gas‐phase elimination of 4‐methoxyl‐1‐chloroburane is attributed to neighboring group participation of the oxygen of the methoxy group in the TS. The theoretical calculations show a good agreement with the reported experimental results. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Role of magnetic shear on the electrostatic current driven ion-cyclotron instability in the presence of parallel electric field

Recent observation and theoretical investigations have led to the significance of electrostatic ion cyclotron (EIC) waves in the electrodynamics of acceleration process. The instability is one of the fundamental of a current carrying magnetized plasma. The EIC instability has the lowest threshold current among the current driven instabilities. On the basis of local analysis where inhomogeneities like the magnetic shear and the finite width current channel, have been ignored which is prevalent in the magnetospheric environment. On the basis of non-local analysis interesting modification has been incorporated by the inclusion of magnetic shear. In this paper we provide an analytical approach for the non-local treatment of current driven electrostatic waves in presence of parallel electric field. The growth rate is significantly influenced by the field aligned electron drift. The presence of electric field enhances the growth of EIC waves while magnetic shear stabilizes the system.     

Supramolecular structure of 5-methyl-5-phenyl hydantoin and hydrogen-bonding patterns in 5,5′-substituted hydantoins

The crystal structure of heterocyclic compound 5-methyl-5-phenyl hydantoin has been determined from X-ray single crystal structural characterization. This material crystallizes in the orthorhombic system and noncentrosymmetric space group P21 (N°4). The crystal packing is governed by N–H···O hydrogen bond-type intermolecular interactions, forming chains and edge-fused 12-membered rings with graph-set C(4) C(5) C22(8) R33(12) in a similar hydrogen-bonding pattern of another chiral 5,5′-substituted hydantoins.     

The Equilibrium Measure for a Nonlocal Dislocation Energy

In this paper we characterize the equilibrium measure for a nonlocal and anisotropic weighted energy describing the interaction of positive dislocations in the plane. We prove that the minimum value of the energy is attained by a measure supported on the vertical axis and distributed according to the semicircle law, a well-known measure that also arises as the minimizer of purely logarithmic interactions in one dimension. In this way we give a positive answer to the conjecture that positive dislocations tend to form vertical walls. This result is one of the few examples where the minimizer of a nonlocal energy is explicitly computed and the only one in the case of anisotropic kernels. © 2018 Wiley Periodicals, Inc.     

Synchronous whirling of spinning homogeneous elastic cylinders: linear and weakly nonlinear analyses

Nonlinear Dynamics - Stationary whirling of slender and homogeneous (continuous) elastic shafts rotating around their axis, with pin–pin boundary condition at the ends, is revisited by...     

Synthesis of Symmetrical and Nonsymmetrical Polyenes by Iterative and Bidirectional Palladium-Catalyzed Cross-Coupling Reactions

Bifunctional unsaturated reagents designed to undergo palladium-catalyzed cross-coupling reactions with complementary polyenyl connective fragments are highly useful for the undoubtedly challenging synthesis of polyenes. The current toolkit of building blocks for the bidirectional formation of Csp²−Csp² single bonds of polyenes includes homo-bisfunctionalized reagents with equal or unequal reactivity (due to steric and/or electronic factors), and hetero-bisfunctionalized counterparts containing either two different nucleophiles, two electrophiles or one of these functionalities and a latent nucleophile that can be unmasked when desired. The combination of these bifunctional linchpin reagents using tactics that modulate the reactivity of each terminus in order to achieve the required connection have streamlined the synthesis of polyenes of great complexity using (iterative) cross-coupling methods for Csp²−Csp² bond formation. Reaction conditions for the Pd-catalyzed cross-coupling reactions are mild and functional-group-tolerant, and therefore these protocols allow to construct the polyene structures using shorter unsaturated reactants with the desired geometries, since in general the products preserve the stereochemical information of the connected cross-coupling partners.     

Derivation of a rod theory for multiphase materials

A rigorous derivation is given of a rod theory for a multiphase material, starting from three-dimensional nonlinear elasticity. The stored energy density is supposed to be nonnegative and to vanish exactly on a set consisting of two copies of the group of rotations SO(3). The two potential wells correspond to the two crystalline configurations preferred by the material. We find the optimal scaling of the energy in terms of the diameter of the rod and we identify the limit, as the diameter goes to zero, in the sense of Γ-convergence.