Number Of Sharp Peaks Research Articles

Quantum transmissivity of one-dimensional mirror structure photonic crystals

In this paper, we have studied the transmission characteristic of one-dimensional mirror structure photonic crystals (MSPCs) (AB)ND1D2D3(BA)N with the quantum theory method. We find there are some sharp peaks (quantum transmissivity T=1) in the PBG of MSPCs, and the number of sharp peaks is added with the increasing of thickness, refractive index and numbers of defect layer, which is beneficial to design the optic filter of multiple channel.

ROLE OF MOLYBDENUM TRIOXIDE ON THERMAL STABILITY OF POLYANILINE NANOCOMPOSITE

Molybdenum trioxide (MoO3) grains were coated with conducting organic polymer of polyaniline. The as-prepared nanocomposite samples were characterized by Fourier transformed infrared (FTIR) spectra, X-ray diffraction (XRD) and Thermogravimetry (TGA). The XRD curves shows that, [Formula: see text] have high crystallinity due to the presence of large number of sharp peaks. From the XRD pattern the particle size is evaluated by using Debye-Scherrer's formula and the average particle size of [Formula: see text] and [Formula: see text] nanocomposites are found to be 46 and 32 nm, respectively. This is clearly observed that the condensed particle size of nanocomposite materials is due to the insertion of metal oxide of molybdenum. The incorporation of metal oxide of MoO3 in polyaniline (Pani) is confirmed by FTIR spectral studies. After de-doping, the characteristic peaks of Pani for all the Pani materials are almost same. This is due to the leaching of metal oxide of MoO3 from Pani. From these observations it is noted that doping–dedoping can also take place in inorganic metal oxides. The thermogram showed a three-step degradation process. The first weight loss step was due to the removal of physisorbed water molecules and moisture. The second minor weight loss step was associated with the removal of dopant from Pani backbone and the slight degradation of benzenoid structure of Pani and their thermal stability is enhanced. The third weight loss step was ascribed to the degradation of quinoid form of Pani. This confirmed the thermal stability of [Formula: see text] nanocomposite system. After degradation above 1000°C, the Pani with MoO3 showed a remaining weight of 8%. This confirmed that incorporation of metal oxide in the Pani nanocomposites is 8%. The enhancement of thermal stability is due to the intercalation of Pani chains into MoO3 in first two step degradation, which is further supported by FTIR and XRD reports. The third step degradation of Pani with MoO3 nanocomposite is loosely bound in organic and inorganic part. Therefore, the organic part is easily decomposed.

Excitons in high-quality CuInS 2 single crystals

High purity single crystals of CuInS 2, grown by the traveling heater method using an indium solvent, were characterised using photoluminescence and reflectance at temperatures from 4.2 to 300 K. A number of sharp peaks, associated with excitons, have been resolved in the near-band-edge region of the optical spectra. The peaks at 1.536 and 1.554 eV, clearly resolved in the reflectance spectra at temperatures up to 240 K, were associated with A and (B, C) free excitons, respectively. Two sharp lines at 1.5348 and 1.5361 eV (near the A exciton) were assigned to the lower and upper branches of exciton–polariton, respectively. The other sharp lines at 1.5309, 1.5255, 1.5228, 1.5203 and 1.5162 eV were related to excitons bound on either shallow donor or acceptor impurities. The temperature variation of the band gap was measured from 4.2 to 300 K.

Isotope effects in the dissociation of the B̃A11 state of SiH2, SiHD, and SiD2 using three-dimensional wave packet propagation

Dissociations after the A 1B1-->B 1A1 photoexcitation of SiH2, SiHD, and SiD2 were studied to investigate excited-state dynamics and effects of the initial vibrational state. The cross section (sigma) for the photodissociation relative to SiH2(B)-->Si(1D)+H2 and the rovibrational population of the H2 fragment were computed using the wave packet propagation technique based on the three-dimensional potential energy surfaces (PESs) of the A and B electronic states and the transition dipole surfaces, which were reported in our previous paper [J. Chem. Phys. 122, 144307 (2005)]. The photodissociation spectrum consists of a broadband and a number of sharp peaks. For SiH2 and SiD2, the sharp peaks correspond to the resonance structure of the vibrational levels of the B state and the broadbands are nearly independent of the photon energy. The broadband for SiHD increases steeply with the photon energy above 30,000 cm(-1). The flux leaving the computational grid for SiH2 and SiD2 consists of at least two components, whereas that for SiHD consists of only a faster component. These large isotope effects were discussed based on the valley to the dissociation channel on PES and the difference in the position of the initial wave packet for three isotopomers.

Magneto-photoluminescence study of radiative recombination in CuInSe 2 single crystals

Radiative recombination processes in CuInSe 2 (CIS) single crystals grown by vertical Bridgman technique were studied using photoluminescence, photoluminescence excitation and magneto-PL. The PL and PLE spectra were measured as functions of temperature (varying from 4.2 to 300 K), excitation intensity, magnetic field (up to 10 T) and the elemental composition. The PL spectra taken at 4.2 K exhibited a complicated structure with a number of sharp peaks in the near-band-edge region associated with free ( E A =1.0416 eV, E B =1.0447 eV ) and bound excitons ( E M1 =1.0386 eV, E M2 =1.0353 eV, E M3 =1.0341 eV, E M4 =1.0324 eV and E M5 =1.0278 eV ) and free-to-bound recombination bands. The binding energies of the bound-excitons were derived. The nature of the defects associated with these excitons and the other observed bands is discussed. A non-linear blue shift toward higher energies was observed in magnetic field for all PL peaks. This shift is in agreement with the exciton energy calculated as a function of field. Field-induced splitting (4.5 meV at 10 T) of a deep band (0.972 eV) band was observed.

Comparison of Experimental to MELTSIM Calculated DNA Melting of the (A+T) Rich Dictyostelium Discoideum Genome: Denaturation Maps Distinguish Exons From Introns

The slime mold, Dictyostelium discoideum, possesses an (A+T) rich eukaryotic genome that is being sequenced in the Human Genome Project. High resolution melting curves of isolated total and fractionated nuclear D. discoideum DNA(AX3 strain) were determined experimentally and are compared to melting curves calculated from GENBANK sequences (1.59% of genome) by the statistical thermodynamics program MELTSIM (1), parameterized for long DNA sequences (2,3). The lower and upper temperature limits of calculated melting agree well with the observed melting of total DNA. The experimental curve is unusual in that it contains a number of sharp peaks. MELTSIM allowed us to calculate positional denaturation maps of D. discoideum GENBANK sequence documents containing the 26S, 5.8S and 17S rDNA gene sequences, a major satellite DNA and repetitive sequence family present in 100–200 copies/nucleus. These denaturation maps contain subtransitions that correspond with a number of the experimentally observed peaks, some of which we show to correspond with rDNA gene enriched CsCl gradient fractions of D. discoideum DNA. MELTSIM calculated curves of coding, intron and flanking sequences indicate that both intron and flanking sequences are extremely (A+T) rich and account for most of the low temperature melting. There is no temperature overlap between thermal stabilities of these sequence domains and those of coding DNA. The latter must satisfy triplet codon constraints of higher (G+C) content. These large stability property differences enable a denaturation mapping feature of MELTSIM to clearly distinguish exon positions from those of introns and flanking DNA in long D. discoideum gene containing sequences.

RESEARCH NOTE The effect of acquisition delay on single- and multiple-quantum proton NMR spectra of liquid crystals

Proton NMR spectra of bulk liquid crystals show broad peaks with very little fine structure. Using a simple technique called acquisition delay, a huge number of sharp peaks can be observed. In this method, an appropriate delay time is inserted after the radio frequency pulse is applied, before the receiver of the spectrometer is turned on; alternatively, the initial part of the free induction decay can be discarded before Fourier transform of the data is carried out. The feature of the spectrum with acquisition delay is strongly dependent on the delay time. Similar characteristics are also observed for multiple-quantum proton spectra, when a delay time is inserted after the second π/2 pulse in the evolution period. Therefore, although the multiple-quantum spectra of a liquid crystal are as broad as its conventional single-quantum spectrum, the use of acquisition delay also filters out the broad components in the multiple-quantum spectra to show fine structures.

Conductance of a quantum wire in a longitudinal magnetic field

We examine the ballistic conductance of a quantum wire in a parallel magnetic field in the presence of several impurities and derive analytic expressions for the transmission coefficient and the conductance in such a system. We show that scattering by impurities leads to a number of sharp peaks near the thresholds of the conductance quantization steps. The number of such peaks is determined by the distance between the impurities and the energy of the scattered particle. We also study the conductivity of a quantum wire in the region where the transport mechanism is diffusive. The conductivity is examined for the case in which charge carriers are scattered by randomly distributed point impurities. We study Shubnikov-de Haas oscillations in such a system. The general oscillation pattern consists of broad minima separated by irregularly spaced sharp peaks of the burst type.

In Situ Monitoring And Control For MBE Growth Of Optoelectronic Devices

Self-organized CdSe/ZnSe quantum dots (QD's) were fabricated on the cleavage-induced GaAs (110) surface in ultra high vacuum (UHV) by molecular beam epitaxy (MBE). CdSe layer showed the Stranski-Krastanow (S-K) growth mode. QW's and QD's emissions originated from the wetting layer and island structures, respectively, were observed in photoluminescence (PL) spectra. This is a evidence of S-K type where island structures are self-formed on the two-dimensional wetting layer as a result of the transition of the growth mode. The state filling effect in the QD's was also observed by employing excitation power dependence on the PL intensity. By using the microscopic PL spectroscopy, the broad PL peak of QD's was resolved into a number of sharp peaks. These peaks are attributed to the recombination of excitons localized at the individual QD's indicating that the fabricated CdSe islands have quasi-zero-dimensional δ-function like density of states.

Quantum waveguide transport with side-branch structures: A recursive algorithm

Electronic conductance of a quantum waveguide with side-branch structures is investigated. We introduce impedance factors for geometric and potential scatterers and develop a recursive algorithm. Impedance factors for several basic unit structures, recursion formulas, and an addition rule are presented with the use of one-dimensional quantum waveguide theory. The impedance factor of a complicated side-branch structure can be evaluated from impedance factors of the individual parts contained in the structure as in the classical resistance-network calculation. This method makes conductance calculations simple since the wave functions of the structures are not required. With this method conductance properties of the quantum waveguides with different periodic side-branch structures (vertical structures) are studied in detail. Electronic conductance of these side-branch modulators manifests band structure with fast oscillating regions and inherent regions. As the number of repeat structures increases, the number of sharp peaks in the oscillating bands increases proportionally while the conductance profiles in the inherent bands remain unchanged. Comparison with the conductance of similar periodic structures along the main wire (horizontal structures) reveals that the oscillating bands and inherent bands of the vertical structure correspond to the transmission bands and forbidden bands of the horizontal structure, respectively.

Excess thermal noise and low-frequency oscillations in capillary flow of non-Newtonian aqueous polymer solutions exhibiting elasticity

Results of thermal noise measurements (frequency range 0.01–1000 Hz) on aqueous solutions of poly(ethylene oxide) and maltose/poly(acrylamide) during capillary flow are reported. The flow of these solutions, both being of the pseudoplastic (shear thinning) type, gave rise to an excess thermal noise exhibiting a 1/fα-frequency distribution. The excess noise level increased with the flow rate. At a critical value of this rate, the noise showed a pulsating character. The corresponding frequency spectra contained a number of sharp peaks, all being multiples of a fundamental frequency of the order of 1 Hz. Increasing the flow rate still higher caused the pulsations to disappear, the excess noise regaining its 1/fα character. The pulsations appear to be associated with the elasticity of the solutions used. Solutions with comparable shear thinning properties but lacking elasticity did not produce such effects. No excess thermal noise was observed with Newtonian solutions of comparable viscosity.

Far infrared spectra of nematic 4-cyano-4′-n-heptylbiphenyl aligne with electric fields

The far i.r. absorption spectrum of 4-cyano-4′-n-heptyl-biphenyl (HCB) in the fied-aligned nematic phase consists of a large number of sharp peaks, most of which are unresolved in the unaligned nematogen; the overall spectral intensity being considerably reduced by polarisation effects as field strength increases.

A medium resolution study of aleene in the vacuum ultraviolet—I

Abstract A vacuum ultraviolet absorption spectra of gaseous allene was investigated with moderately high resolution down to 1160 A. Four broad, molecular bands were observed along with a large number of sharp peaks that are either vibrational or Rydberg in character. The vibrational separations were noted for the first three of the broad bands with averages of 580, 1100,1130, 960, 682 cm −1 and two major Rydberg series were found with Rydberg corrections of 0.92 and 0.37 converging to the same limit of 80,788 ± 25 cm −1 (10.016 ± 0.002 eV).

Hydrogen bonding in the vapour phase: an unusual type of infrared band

Association bands, due to vibrations of the hydrogen halides modified by hydrogen bonding, have been measured in the near infrared spectra of mixtures of alkyl cyanides with hydrogen chloride or deuterium chloride in the vapour phase. The vibration frequencies of the hydrogen bonds have been estimated. The association band found with mixtures of methyl cyanide and hydrogen chloride, or deutero derivatives of each of these molecules, shows a broad contour upon which a number of sharp peaks are superposed at the lower frequency side. These peaks have been interpreted as being due to an agglomeration of P lines near the band head in each of a series of hot bands which accompany the association band, and which arise from transitions from higher levels of a bending mode of low frequency. The latter appears to have a frequency in the range 20 to 60 cm -1 . The spectral analysis suggests that the excitation of the hydrogen halide stretching vibration leads to a shortening of the hydrogen bond.

Huancayo Magnetic Observatory, January to March, 1944

(Latitude 12° 02′.7 S., longitude 75° 20′.4 or 5h 01m.4 W. of Gr.)February 7—A short magnetic disturbance was recorded beginning at 12h GMT, February 7. It was ushered in by a decrease of about 150 gammas in H during the first hour and followed by a number of sharp peaks and bays till after 18h, and then continued for about two hours more in a mild form. D and Z were also noticeably disturbed during the period of activity in H. H was somewhat below normal for the next day. The total range in H was 180 gammas during the disturbed period.