211 research outputs found
Coherent Acoustic Perturbation of Second-Harmonic-Generation in NiO
We investigate the structural and magnetic origins of the unusual ultrafast
second-harmonicgeneration (SHG) response of femtosecond-laser-excited nickel
oxide (NiO) previously attributed to oscillatory reorientation dynamics of the
magnetic structure induced by d-d excitations. Using time-resolved x-ray
diffraction from the (3/2 3/2 3/2) magnetic planes, we show that changes in the
magnitude of the magnetic structure factor following ultrafast optical
excitation are limited to = 1.5% in the first 30 ps. An
extended investigation of the ultrafast SHG response reveals a strong
dependence on wavelength as well as characteristic echoes, both of which give
evidence for an acoustic origin of the dynamics. We therefore propose an
alternative mechanism for the SHG response based on perturbations of the
nonlinear susceptibility via optically induced strain in a spatially confined
medium. In this model, the two observed oscillation periods can be understood
as the times required for an acoustic strain wave to traverse one coherence
length of the SHG process in either the collinear or anti-collinear geometries.Comment: 26 pages, 7 figure
Stan Scheller: The Forerunner of Clinical Studies on Using Propolis for Poor and Chronic Nonhealing Wounds
For hundreds of years poor and chronic nonhealing wounds have constituted a serious problem to medicine. What is more, treating such wounds is an expensive let alone a long-lasting process. The following paper describes Professor Scheller's achievements in using propolis for poor and chronic non-healing wounds. The authors' intention was to present the results connected with the use of the ethanolic extract propolis, in the treatment of patients suffering from burns, venous crural ulceration, local sacral bone pressure ulcers, suppurative osteitis and arthritis, suppurative postoperative local wound complications, and infected traumatic wounds
Ultrafast relaxation dynamics of the antiferrodistortive phase in Ca doped SrTiO3
The ultrafast dynamics of the octahedral rotation in Ca:SrTiO3 is studied by
time resolved x-ray diffraction after photo excitation over the band gap. By
monitoring the diffraction intensity of a superlattice reflection that is
directly related to the structural order parameter of the soft-mode driven
antiferrodistortive phase in Ca:SrTiO3, we observe a ultrafast relaxation on a
0.2 ps timescale of the rotation of the oxygen octahedron, which is found to be
independent of the initial temperaure despite large changes in the
corresponding soft-mode frequency. A further, much smaller reduction on a
slower picosecond timescale is attributed to thermal effects. Time-dependent
density-functional-theory calculations show that the fast response can be
ascribed to an ultrafast displacive modification of the soft-mode potential
towards the normal state, induced by holes created in the oxygen 2p states
Ultrafast Laser-Induced Melting of Long-Range Magnetic Order in Multiferroic TbMnO3
We performed ultrafast time-resolved near-infrared pump, resonant soft X-ray
diffraction probe measurements to investigate the coupling between the
photoexcited electronic system and the spin cycloid magnetic order in
multiferroic TbMnO3 at low temperatures. We observe melting of the long range
antiferromagnetic order at low excitation fluences with a decay time constant
of 22.3 +- 1.1 ps, which is much slower than the ~1 ps melting times previously
observed in other systems. To explain the data we propose a simple model of the
melting process where the pump laser pulse directly excites the electronic
system, which then leads to an increase in the effective temperature of the
spin system via a slower relaxation mechanism. Despite this apparent increase
in the effective spin temperature, we do not observe changes in the wavevector
q of the antiferromagnetic spin order that would typically correlate with an
increase in temperature under equilibrium conditions. We suggest that this
behavior results from the extremely low magnon group velocity that hinders a
change in the spin-spiral wavevector on these time scales.Comment: 9 pages, 4 figure
Disentangling charge and structural contributions during coherent atomic motions studied by ultrafast resonant x-ray diffraction
We report on the ultrafast dynamics of charge order and structural response
during the photoinduced suppression of charge and orbital order in a
mixed-valence manganite. Employing femtosecond time-resolved resonant x-ray
diffraction below and at the Mn K absorption edge, we present a method to
disentangle the transient charge order and structural dynamics in thin films of
Pr0.5Ca0.5MnO3. Based on the static resonant scattering spectra, we extract the
dispersion correction of charge ordered Mn3+ and Mn4+ ions, allowing us to
separate the transient contributions of purely charge order from structural
contributions to the scattering amplitude after optical excitation. Our finding
of a coherent structural mode at around 2.3 THz, which primarily modulates the
lattice, but does not strongly affect the charge order, confirms the picture of
the charge order being the driving force of the combined charge, orbital and
structural transition
Temperature-dependent electron-phonon coupling in LaSrCuO probed by femtosecond X-ray diffraction
The strength of the electron-phonon coupling parameter and its evolution
throughout a solid's phase diagram often determines phenomena such as
superconductivity, charge- and spin-density waves. Its experimental
determination relies on the ability to distinguish thermally activated phonons
from those emitted by conduction band electrons, which can be achieved in an
elegant way by ultrafast techniques. Separating the electronic from the
out-of-equilibrium lattice subsystems, we probed their re-equilibration by
monitoring the transient lattice temperature through femtosecond X-ray
diffraction in LaSrCuO single crystals with =0.1 and 0.21.
The temperature dependence of the electron-phonon coupling is obtained
experimentally and shows similar trends to what is expected from the
\textit{ab-initio} calculated shape of the electronic density-of-states near
the Fermi energy. This study evidences the important role of band effects in
the electron-lattice interaction in solids, in particular in superconductors
Global Cortical Atrophy Is Associated with an Unfavorable Outcome in Stroke Patients on Oral Anticoagulation.
INTRODUCTION
Measures of cerebral small vessel disease (cSVD), such as white matter hyperintensities (WMH) and cerebral microbleeds (CMB), are associated with an unfavorable clinical course in stroke patients on oral anticoagulation (OAC) for atrial fibrillation (AF). Here, we investigated whether similar findings can be observed for global cortical atrophy (GCA).
METHODS
Registry-based prospective observational study of 320 patients treated with OAC following AF stroke. Patients underwent magnetic resonance imaging (MRI) allowing assessment of GCA. Using the simplified visual Pasquier scale, the severity of GCA was categorized as follows: 0: no atrophy, 1: mild atrophy; 2: moderate atrophy, and 3: severe atrophy. Using adjusted logistic and Cox regression analysis, we investigated the association of GCA using a composite outcome measure, comprising: (i) recurrent acute ischemic stroke (IS); (ii) intracranial hemorrhage (ICH); and (iii) death.
RESULTS
In our time to event analysis after adjusting for potential confounders (i.e., WMH, CMB, age, sex, diabetes, arterial hypertension, coronary heart disease, hyperlipidemia, and antiplatelet use), GCA was associated with an increased risk for the composite outcome in all three degrees of atrophy (grade 1: aHR 3.95, 95% CI 1.34-11.63, p = 0.013; grade 2: aHR 3.89, 95% CI 1.23-12.30, p = 0.021; grade 3: aHR 4.16, 95% CI 1.17-14.84, p = 0.028).
CONCLUSION
GCA was associated with our composite outcome also after adjusting for other cSVD markers (i.e., CMB, WMH) and age, indicating that GCA may potentially serve as a prognostic marker for stroke patients with atrial fibrillation on oral anticoagulation
Synthesis and characterization of Sn‑doped TiO2 flm for antibacterial applications
Simple sol–gel method has been exploited to deposit Sn-doped TiO2 thin flms on glass substrates. The resultant coatings
were characterized by X-ray difraction (XRD), UV–visible techniques (UV–Vis), Fourier transform infrared spectroscopy
(FTIR), and photoluminescence analysis (PL). The XRD pattern reveals an increase in crystallite size of the prepared samples
with the increasing doping concentration. A decrease in doping concentrating resulted in the decrease in bandgap values. The
diferent chemical bonds on these flms were identifed from their FTIR spectra. The photoluminescence analysis shows an
increase in the emission peak intensity with increasing dopant concentration, and this can be attributed to the efect created
due to surface states. The prepared samples were tested as antibacterial agent toward both Gram-positive and Gram-negative
bacteria like S.aureus (Staphylococcus aureus) and E.coli (Escherichia coli), respectively. The size of the inhibition zones
indicates that the sample shows maximum inhibitory property toward E.coli when compared to S.aureus
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