Nonlinear frequency response of a moving grating with an applied field in bismuth silicon oxide

A fully nonlinear frequency response of a moving grating in bismuth silicon oxide, including the effects of an applied electric field, is modeled by solution of the time-dependent Kukhtarev equations for photorefractive materials. The numerical results are used to define fully the nonlinear response function F(m)=a(-1)[1-exp(-am)], where m is the modulation index in the intensity pattern, to yield the unknown quantity a over a broad range of detuning frequencies f . For low f, the response is superlinear with a<0, and for relatively large f it is sublinear with a>0 . In the midrange we predict, for the first time to our knowledge, a characteristic frequency f(l) at which a=0 and the response is linear, that is, F(m) approximately m, despite the presence of nonlinearly generated higher harmonics of the fundamental grating wave number. In view of this linear behavior, writing a hologram at the linear-response frequency f(l) might permit a more faithful reproduction of an object than that which is possible by writing at the frequency of maximum response at the resonance.     

Cumulant functions in optical coherence theory

Cumulant functions are introduced to describe the statistical state of a radiation field. These functions are simply related to the optical coherence functions but have some interesting features. It is shown that if the cumulant functions of all orders greater than some numberN ₀ vanish then they also vanish for all orders greater than 2. Thermal field is the only field having this property. This property holds whether the field is described by a classical stochastic process or by a quantum density operator. Further the particular operator ordering used in defining these cumulant functions for the quantized field affects only the second order cumulant function. To describe the statistical state of a vector field such as partially polarized or unpolarized radiation, one would need to introduce cumulant tensors.     

Gas phase activation energy for unimolecular dissociation of biomolecular ions determined by focused RAdiation for gaseous multiphoton ENergy transfer (FRAGMENT)

We present a novel approach for the determination of activation energy for the unimolecular dissociation of a large (>50 atoms) ion, based on measurement of the unimolecular dissociation rate constant as a function of continuous-wave CO(2) laser intensity. Following a short ( approximately 1 s) induction period, CO(2) laser irradiation produces an essentially blackbody internal energy distribution, whose 'temperature' varies inversely with laser intensity. The only currently available method for measuring such activation energies is blackbody infrared radiative dissociation (BIRD). Compared with BIRD, FRAGMENT: (a) eliminates the need to heat the surrounding ion trap and vacuum chamber to each of several temperatures (each requiring hours for temperature equilibration); (b) offers a three-fold wider range of effective blackbody temperature; and (c) extends the range of applications to include initially cold ions (e.g., gas-phase H/D exchange). Our FRAGMENT-determined activation energy for dissociation of protonated bradykinin, 1.2 +/- 0.1 eV, agrees within experimental error to the value, 1.3 +/- 0.1 eV, previously reported by Williams et al. from BIRD experiments. Copyright 1999 John Wiley & Sons, Ltd.     

Quantitative electrospray ionization mass spectrometric studies of ternary complexes of amino acids with Cu(2+) and phenanthroline

Electrospray ionization (ESI) mass spectra of ternary complexes of Cu(2+) and 1,10-phenanthroline with the 20 essential amino acids (AA) were investigated quantitatively. Non-basic amino acids formed singly charged complexes of the [Cu(AA - H)phen](+) type. Lysine (Lys) and arginine (Arg) formed doubly charged complexes of the [Cu(HAA - H)phen](2+) type. Detection limits were determined for the complexes of phenylalanine (Phe), glutamic acid (Glu) and Arg, which were at low micromolar or submicromolar concentrations under routine conditions. Detection limits of low nanomolar concentrations are possible for amino acids with hydrophobic side-chains (Phe, Tyr, Trp, Leu, Ile) as determined for Phe. The efficiencies for the formation by ESI of gaseous [Cu(AA - H)phen](+) ions were determined and correlated with the acid-base properties of the amino acids, ternary complex stability constants and amino acid hydrophobicities expressed as the Bull-Breese indices (DeltaF). A weak correlation was found between DeltaF and the ESI efficiencies for the formation of gaseous [Cu(AA - H)phen](+) [Cu(HAA - H]phen](2+) and [AA + H](+) ions that showed that amino acids with hydrophobic side-chains were ionized more efficiently. In the ESI of binary and ternary amino acid mixtures, the formation of gas-phase Cu-phen complexes of amino acids with hydrophobic side-chains was enhanced in the presence of complexes of amino acids with polar or basic side-chains. An interesting enhancement of the ESI formation of [Cu(Glu - H)phen](+) was observed in mixtures. The effect is explained by ion-cluster formation at the droplet interface that results in enhanced desorption of the glutamic acid complex.     

A simple organic reaction mediates the crystallization of the inorganic nanocluster [Ga13(mu3-OH)6(mu2-OH)18(H2O)24](NO3)15

We report the single-crystal structure of an inorganic gallium cluster [Ga13(mu3-OH)6(mu2-OH)18(H2O)24](NO3)15.6H2O prepared using a simple organic reaction to drive the formation of the crystalline inorganic cluster.     

Time-reversed information transmission

Tolman's paradox forbidding time-reversed information transmission is nonexistent and rests only on our ingrained thought processes involving hidden, unnecessary assumptions. When the assumption of a passive channel is removed, the paradox cannot be derived and information can flow intermittently or nondeterministically from the future over a simple computer with at least one independent decision-making component.     

Facile synthesis of the tridecameric Al13 nanocluster Al13(mu3-OH)6(mu2-OH)18(H2O)24(NO3)15

Treatment of aluminum nitrate with an organic nitroso-containing compound yields the "flat", tridecameric nanocluster Al 13(mu 3-OH) 6(mu 2-OH) 18(H 2O) 24(NO 3) 15 ( Al 13 ) in good yield on a preparative scale under ambient conditions. Synthetic procedures yielding two different single-crystal forms of the Al 13 cation with two varying counterion compositions are described.