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41.
In this paper we study smooth complex projective varieties X containing a Grassmannian of lines ${{\mathbb G}(1, r)}$ which appears as the zero locus of a section of a rank two nef vector bundle E. Among other things we prove that the bundle E cannot be ample. 相似文献
42.
S. Rout N. Popovici S. Dalui M.L. Paramês R.C. da Silva A.J. Silvestre O. Conde 《Current Applied Physics》2013,13(4):670-676
This paper reports on the structural and optical properties of Co-doped TiO2 thin films grown onto (0001)Al2O3 substrates by non-reactive pulsed laser deposition (PLD) using argon as buffer gas. It is shown that by keeping constant the substrate temperature at as low as 310 °C and varying only the background gas pressure between 7 Pa and 70 Pa, it is possible to grow either epitaxial rutile or pure anatase thin films, as well as films with a mixture of both polymorphs. The optical band gaps of the films are red shifted in comparison with the values usually reported for undoped TiO2, which is consistent with n-type doping of the TiO2 matrix. Such band gap red shift brings the absorption edge of the Co-doped TiO2 films into the visible region, which might favour their photocatalytic activity. Furthermore, the band gap red shift depends on the films’ phase composition, increasing with the increase of the Urbach energy for increasing rutile content. 相似文献
43.
J.S. Blázquez M. Millán C.F. Conde V. Franco A. Conde S. Lozano-Pérez 《Journal of Non》2008,354(47-51):5135-5137
Specific heat at constant pressure, CP, was measured on amorphous, nanocrystalline and fully crystalline samples of Fe60Co18Nb6B16 alloy. Magnetic and calorimetric measurements agree, describing a continuously decreasing Curie temperature of the amorphous phase. A clear enhancement of CP over the Dulong–Pettit limit has been observed (from 14% to 25 %). Part of the enhancement is due to magnetic (mainly amorphous phase) and electronic contributions, although an excess volume can be inferred from the high value of the slope of CP versus temperature. 相似文献
44.
DC Muddiman AP Null JC Hannis 《Rapid communications in mass spectrometry : RCM》1999,13(12):1201-1204
Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) has been used to determine the mass of a double-stranded 500 base-pair (bp) polymerase chain reaction (PCR) product with an average theoretical mass of the blunt-ended (i.e. unadenylated) species of 308 859.35 Da. The PCR product was generated from the linearized bacteriophage Lambda genome which is a double-stranded template. Utilization of ethanol precipitation in tandem with a rapid microdialysis step to purify and desalt the PCR product was crucial to obtain a precise mass measurement. The PCR product (0.8 pmol/μL) was electrosprayed from a solution containing 75% acetonitrile, 25 mM piperidine, and 25 mM imidazole and was infused at a rate of 200 nL/min. The average molecular mass and the corresponding precision were determined using the charge-states ranging from 172 to 235 net negative charges. The experimental mass and corresponding precision (reported as the 95% confidence interval of the mean) was 309 406 +/- 27 Da (87 ppm). The mass accuracy was compromised due to the fact that the PCR generates multiple products when using Taq polymerase due to the non-template directed 3'-adenylation. This results in a mixture of three PCR products with nearly identical mass (i.e. blunt-ended, mono-adenylated and di-adenylated) with unknown relative abundances that were not resolved in the spectrum. Thus, the experimental mass will be a weighted average of the three species which, under our experimental conditions, reflects a nearly equal concentration of the mono- and di-adenylated species. This report demonstrates that precise mass measurements of PCR products up to 309 kDa (500 bp) can be routinely obtained by ESI-FTICR requiring low femtomole amounts. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
45.
D. Taqqu F. Biraben C.A.N. Conde T.W. Hänsch F.J. Hartmann P. Hauser P. Indelicato P. Knowles F. Kottmann F. Mulhauser C. Petitjean R. Pohl P. Rabinowitz R. Rosenfelder J.M.F. Santos W. Schott L.M. Simons J.F.C.A. Veloso 《Hyperfine Interactions》1999,119(1-4):311-315
The muonic hydrogen atom in the 2s state provides the possibility of achieving high precision laser spectroscopy experiments
from which a high precision value of the proton radius can be deduced. This will ultimately allow an increased precision in
the test of QED in bound systems. Important progress has been made in recent years in the ability to stop muons in a low pressure
gas target and in the understanding of the 2s-metastability in muonic hydrogen. As a consequence the 2s–2p laser spectroscopy
experiment is now feasible and we present here the basic experimental concept considered by our collaboration.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
46.
The execution of a given project, with a number of interrelated tasks due to precedence constraints, represents a challenge when one must to control the available resources and the compromised due dates. In this paper, we analyse this problem under uncertain individual task completing times, specifically, we will assume that a given range, for the admissible values of each individual completing time, is available. Taking into account that the precedence relations between tasks must be preserved, each realization of the admissible execution times for the set of tasks will define a new scenario determining the ending time for the project and the subset of critical tasks. 相似文献
47.
S.C. Paticopoulos R. Caballero-Flores V. Franco J.S. Blázquez A. Conde K.E. Knipling M.A. Willard 《Solid State Communications》2012,152(16):1590-1594
Recent calculations have shown that the refrigerant capacity (RC) of magnetic refrigerants can be enhanced using multiphase materials or composites, which expand the temperature range over which a significant magnetic entropy change can be obtained. This work is a systematic experimental validation of the improvement of RC (RCI) using layered composites comprised of two Fe88?2yCoyNiyZr7B4Cu1 amorphous alloy constituents, with y=8.25 and y=11 compositions. RCI has a nonmonotonic dependence on the applied magnetic field H and the fraction x of the two constituent phases. In contrast to common assumptions, the composite has a smaller RCI than its constituent phases for small values of H and x, and there are critical values of each for which RCI is maximized. This work demonstrates the outstanding agreement between the experimental results and the continuous curves predicted by numerical calculations, indicating that this approach can be used to design magnetic refrigerant materials with enhanced magnetocaloric response for moderate magnetic fields. 相似文献
48.
Denis David Christian Godet Hussein Sabbah Soraya Ababou-Girard Francine Solal Virginia Chu João Pedro Conde 《Journal of Non》2012,358(17):2019-2022
The near-surface dielectric function ε(?ω) of hydrogenated amorphous silicon (a-Si:H) films has been derived from X-ray photoelectron energy-loss spectra, over the energy range 0–40 eV. Removal of low lying single-electron excitations is a prerequisite step to proceed to the derivation of the single plasmon energy loss function Im[? 1/ε(?ω)] due to collective electron oscillations. Several methods are compared to separate interband transitions from bulk or surface plasmons excitation. The shape of interband excitation loss in the range 1–10 eV can be described by a Henke function; alternatively, its removal using a sigmoid weighting function is a low-noise and reliable method. After deconvolution of multiple plasmon losses and self-consistent elimination of surface plasmon excitation, the single plasmon loss distribution allows recovery of optical (ellipsometry) data measured in the near-UV to visible range. 相似文献
49.
50.
Montero R Conde ÁP Ovejas V Castaño F Longarte A 《The journal of physical chemistry. A》2012,116(11):2698-2703
The relaxation dynamics of the isolated indole molecule has been tracked by femtosecond time-resolved ionization. The excitation region explored (283-243 nm) covers three excited states: the two ππ* L(b) and L(a) states, and the dark πσ* state with dissociative character. In the low energy region (λ > 273 nm) the transients collected reflect the absorption of the long living L(b) state. The L(a) state is met 1000-1500 cm(-1) above the L(b) origin, giving rise to an ultrafast lifetime of 40 fs caused by the internal conversion to the lower L(b) minimum through a conical intersection. An additional ~400 fs component, found at excitation wavelengths shorter than 263 nm, is ascribed to dynamics along the πσ* state, which is likely populated through coupling to the photoexcited L(a) state. The study provides a general view of the indole photophysics, which is driven by the interplay between these three excited surfaces and the ground state. 相似文献