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1.
J Chem Phys ; 139(18): 184309, 2013 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-24320276

RESUMO

Nonradiative energy dissipation in electronically excited polyatomic molecules proceeds through conical intersections, loci of degeneracy between electronic states. We observe a marked enhancement of laser-induced double ionization in the vicinity of a conical intersection during a non-radiative transition. We measured double ionization by detecting the kinetic energy of ions released by laser-induced strong-field fragmentation during the ring-opening transition between 1,3-cyclohexadiene and 1,3,5-hexatriene. The enhancement of the double ionization correlates with the conical intersection between the HOMO and LUMO orbitals.

2.
Phys Rev Lett ; 108(25): 253006, 2012 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-23004597

RESUMO

We report the first study of UV-induced photoisomerization probed via core ionization by an x-ray laser. We investigated x-ray ionization and fragmentation of the cyclohexadiene-hexatriene system at 850 eV during the ring opening. We find that the ion-fragmentation patterns evolve over a picosecond, reflecting a change in the state of excitation and the molecular geometry: the average kinetic energy per ion fragment and H(+)-ion count increase as the ring opens and the molecule elongates. We discuss new opportunities for molecular photophysics created by optical pump x-ray probe experiments.


Assuntos
Alcenos/química , Ciclização/efeitos da radiação , Cicloexenos/química , Polienos/química , Processos Fotoquímicos , Espectrofotometria Ultravioleta , Termodinâmica , Raios X
3.
J Phys Chem A ; 116(11): 2758-63, 2012 Mar 22.
Artigo em Inglês | MEDLINE | ID: mdl-22082319

RESUMO

We have studied the photoinduced isomerization from 1,3-cyclohexadiene to 1,3,5-hexatriene in the presence of an intense ultrafast laser pulse. We find that the laser field maximally suppresses isomerization if it is both polarized parallel to the excitation dipole and present 50 fs after the initial photoabsorption, at the time when the system is expected to be in the vicinity of a conical intersection that mediates this structural transition. A modified ab initio multiple spawning (AIMS) method shows that the laser induces a resonant coupling between the excited state and the ground state, i.e., a light-induced conical intersection. The theory accounts for the timing and direction of the effect.

4.
Phys Rev Lett ; 107(14): 143001, 2011 Sep 30.
Artigo em Inglês | MEDLINE | ID: mdl-22107187

RESUMO

Transitions between Rydberg states of Ca atoms, in a pulsed, supersonic atomic beam, are directly detected by chirped-pulse millimeter-wave spectroscopy. Broadband, high-resolution spectra with accurate relative intensities are recorded instantly. Free induction decay (FID) of atoms, polarized by the chirped pulse, at their Rydberg-Rydberg transition frequencies, is heterodyne detected, averaged in the time domain, and Fourier transformed into the frequency domain. Millimeter-wave transient nutations are observed, and the possibility of FID evolving to superradiance is discussed.

5.
Health Informatics J ; 26(3): 2148-2158, 2020 09.
Artigo em Inglês | MEDLINE | ID: mdl-31969046

RESUMO

Kinsa Inc. sells Food and Drug Administration-cleared smart thermometers, which synchronize with a mobile application, and may aid influenza forecasting efforts. We compare smart thermometer and mobile application data to regional influenza and influenza-like illness surveillance data from the California Department of Public Health. We evaluated the correlation between the regional California surveillance data and smart thermometer data, tested the hypothesis that smart thermometer readings and symptom reports provide regionally specific predictions, and determined whether smart thermometer and mobile application improved disease forecasts. Smart thermometer readings are highly correlated with regional surveillance data, are more predictive of surveillance data for their own region and season than for other times and places, and improve predictions of influenza, but not predictions of influenza-like illness. These results are consistent with the hypothesis that smart thermometer readings and symptom reports reflect underlying disease transmission in California. Data from such cloud-based devices could supplement syndromic influenza surveillance data.


Assuntos
Influenza Humana , Aplicativos Móveis , Previsões , Humanos , Influenza Humana/diagnóstico , Influenza Humana/epidemiologia , Estações do Ano , Termômetros
6.
J Chem Phys ; 131(6): 064301, 2009 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-19691382

RESUMO

The Stark effect in molecular Rydberg states is qualitatively different from the Stark effect in atomic Rydberg states because of the anisotropy of the ion core and the existence of rotational and vibrational degrees of freedom. These uniquely molecular features cause the electric-field-induced decoupling of the Rydberg electron from the body frame to proceed in several stages in a molecule. Because the transition dipole moment among the same-n* Rydberg states is much larger than the permanent dipole moment of the ion core, the decoupling of the Rydberg electron from the ion core proceeds gradually. In the first stage, analyzed in detail in this paper, l and N are mixed by the external electric field, while N+ is conserved. In the further stages, as the external electric field increases, N+, n*, and v+ are expected to undergo mixing. We have characterized these stages in n*=13, v+=1 states of CaF. The large permanent dipole moment of CaF+ makes CaF qualitatively different from the other molecules in which the Stark effect in Rydberg states has been described (H2, Na2, Li2, NO, and H3) and makes it an ideal testbed for documenting the competition between the external and CaF+ dipole electric fields. We use the weak-field Stark effect to gain access to the lowest-N rotational levels of f, g, and h states and to assign their actual or nominal N+ quantum number. Lowest-N rotational levels provide information needed to disentangle the short-range and long-range interactions between the Rydberg electron and the ion core. We diagonalize an effective Hamiltonian matrix to determine the l-characters of the 3 < or = l < or = 5 core-nonpenetrating 2Sigma+ states and to characterize their mixing with the core-penetrating states. We conclude that the mixing of the l=4, N-N+=-4(g(-4)) state with lower-l 2Sigma+ states is stronger than documented in our previous multichannel quantum defect theory and long-range fits to zero-field spectra.

7.
Nat Commun ; 6: 8199, 2015 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-26354002

RESUMO

Rapid proton migration is a key process in hydrocarbon photochemistry. Charge migration and subsequent proton motion can mitigate radiation damage when heavier atoms absorb X-rays. If rapid enough, this can improve the fidelity of diffract-before-destroy measurements of biomolecular structure at X-ray-free electron lasers. Here we study X-ray-initiated isomerization of acetylene, a model for proton dynamics in hydrocarbons. Our time-resolved measurements capture the transient motion of protons following X-ray ionization of carbon K-shell electrons. We Coulomb-explode the molecule with a second precisely delayed X-ray pulse and then record all the fragment momenta. These snapshots at different delays are combined into a 'molecular movie' of the evolving molecule, which shows substantial proton redistribution within the first 12 fs. We conclude that significant proton motion occurs on a timescale comparable to the Auger relaxation that refills the K-shell vacancy.

8.
IEEE Trans Pattern Anal Mach Intell ; 32(11): 1994-2005, 2010 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-20847389

RESUMO

Groupwise image registration algorithms seek to establish dense correspondences between sets of images. Typically, they involve iteratively improving the registration between each image and an evolving mean. A variety of methods have been proposed, which differ in their choice of objective function, representation of deformation field, and optimization methods. Given the complexity of the task, the final accuracy is significantly affected by the choices made for each component. Here, we present a groupwise registration algorithm which can take advantage of the statistics of both the image intensities and the range of shapes across the group to achieve accurate matching. By testing on large sets of images (in both 2D and 3D), we explore the effects of using different image representations and different statistical shape constraints. We demonstrate that careful choice of such representations can lead to significant improvements in overall performance.


Assuntos
Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Reconhecimento Automatizado de Padrão/métodos , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Algoritmos , Biometria/métodos , Encéfalo/anatomia & histologia , Criança , Face/anatomia & histologia , Humanos , Imageamento Tridimensional/métodos , Armazenamento e Recuperação da Informação , Pessoa de Meia-Idade , Adulto Jovem
9.
J Chem Phys ; 128(1): 014301, 2008 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-18190190

RESUMO

The polarization dependence of transition intensities in multiple resonance spectroscopic experiments can provide information useful for making rotational assignments. A formalism to describe the polarization dependence of transition intensities in multiple resonance experiments, particularly for cases when two rotational/fine structure quantum numbers are needed to specify the state of the system, is presented. The formalism is presented in a form usable both when the transitions between the underlying fine structure components are experimentally resolved, as well as when they are unresolved, to form composite lines. This sort of treatment is necessary for cases when the two quantum numbers that specify the fine structure differ significantly, such as is the case at low N, when the difference between J and N becomes comparable to the value of J. Ratios of transition intensities in different experimentally convenient polarization arrangements are evaluated for the case of composite N transitions formed by combining the spin components of a doublet system. The formalism is expressed in a form easily extendable to accommodate experimental cases of more than two excitation steps, or a combination of excitation steps and an external static electric field. This polarization diagnostic has been experimentally applied to assign spectral features in double resonance Rydberg spectra of CaF.

10.
J Chem Phys ; 128(19): 194301, 2008 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-18500859

RESUMO

Observation and analysis of the f([script-l]=3), g([script-l]=4), and h([script-l]=5) Rydberg series of CaF in the range 13

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