1,450 research outputs found
Optimal generation of spatially coherent soft X-ray isolated attosecond pulses in a gas-filled waveguide using two-color synthesized laser pulses
We numerically demonstrate the generation of intense, low-divergence soft X-ray isolated attosecond pulses in a gas-filled hollow waveguide using synthesized few-cycle two-color laser waveforms. The waveform is a superposition of a fundamental and its second harmonic optimized such that highest harmonic yields are emitted from each atom. We then optimize the gas pressure and the length and radius of the waveguide such that bright coherent high-order harmonics with angular divergence smaller than 1 mrad are generated, for photon energy from the extreme ultraviolet to soft X-rays. By selecting a proper spectral range enhanced isolated attosecond pulses are generated. We study how dynamic phase matching caused by the interplay among waveguide mode, neutral atomic dispersion, and plasma effect is achieved at the optimal macroscopic conditions, by performing time-frequency analysis and by analyzing the evolution of the driving laser’s electric field during the propagation. Our results, when combined with the on-going push of high-repetition-rate lasers (sub- to few MHz’s) may eventually lead to the generation of high-flux, low-divergence soft X-ray tabletop isolated attosecond pulses for applications.Fundamental Research Funds for the Central Universities of China (Grant No. 30916011207)United States. Department of Energy. Office of Science (Grant No. DE-FG02-86ER13491)United States. Air Force Office of Scientific Research (Grant No. FA9550- 14-1-0255
Enzyme Attached on Polymeric Micelles as a Nanoscale Reactor
Similar to what lipase does, a surface-active enzyme was developed by attaching peroxidase on combshaped polymaleic anhydride-alt-1-tetradecene (PMA-TD) in a microemulsion system composed of n-butyl acetate and buffer solution, and its catalytic characteristics of polyphenol synthesis were investigated in an aqueous solution. The modified peroxidase with PMA-TD tended to form self-assembled aggregates like micelles in the aqueous solution and could be concentrated at solvent/water interfaces without unfolding of the enzyme. The efficiency of conversion of 2,4-dichlorophenol to phenolic oligomers was approximately 2-fold improved with the modified peroxidase compared to native peroxidase. The K m and V max values for the modified peroxidase were 1.5-fold lower and 2-fold higher, respectively. The hydrodynamic diameter of the micelle on the modified peroxidase increased with the reaction time, indicating that phenolic products were accumulated in the hydrophobic interior of micelles. In addition, the molecular weight (MW) of phenolic polymers was much larger in the system with the modified peroxidase. These observations implied that the modified peroxidase with hydrophobic side chains formed micellar structures by solubilization of phenolic products and further polymerization reaction could occur in the hydrophobic interior of the micelles
Enzyme Attached on Polymeric Micelles as a Nanoscale Reactor
Similar to what lipase does, a surface-active enzyme was developed by attaching peroxidase on combshaped polymaleic anhydride-alt-1-tetradecene (PMA-TD) in a microemulsion system composed of n-butyl acetate and buffer solution, and its catalytic characteristics of polyphenol synthesis were investigated in an aqueous solution. The modified peroxidase with PMA-TD tended to form self-assembled aggregates like micelles in the aqueous solution and could be concentrated at solvent/water interfaces without unfolding of the enzyme. The efficiency of conversion of 2,4-dichlorophenol to phenolic oligomers was approximately 2-fold improved with the modified peroxidase compared to native peroxidase. The K m and V max values for the modified peroxidase were 1.5-fold lower and 2-fold higher, respectively. The hydrodynamic diameter of the micelle on the modified peroxidase increased with the reaction time, indicating that phenolic products were accumulated in the hydrophobic interior of micelles. In addition, the molecular weight (MW) of phenolic polymers was much larger in the system with the modified peroxidase. These observations implied that the modified peroxidase with hydrophobic side chains formed micellar structures by solubilization of phenolic products and further polymerization reaction could occur in the hydrophobic interior of the micelles
Experimental observation of hidden Berry curvature in inversion-symmetric bulk 2H-WSe2
We investigate the hidden Berry curvature in bulk 2H-WSe2 by utilizing the
surface sensitivity of angle resolved photoemission (ARPES). The symmetry in
the electronic structure of transition metal dichalcogenides is used to
uniquely determine the local orbital angular momentum (OAM) contribution to the
circular dichroism (CD) in ARPES. The extracted CD signals for the K and K'
valleys are almost identical but their signs, which should be determined by the
valley index, are opposite. In addition, the sign is found to be the same for
the two spin-split bands, indicating that it is independent of spin state.
These observed CD behaviors are what are expected from Berry curvature of a
monolayer of WSe2. In order to see if CD-ARPES is indeed representative of
hidden Berry curvature within a layer, we use tight binding analysis as well as
density functional calculation to calculate the Berry curvature and local OAM
of a monolayer WSe2. We find that measured CD-ARPES is approximately
proportional to the calculated Berry curvature as well as local OAM, further
supporting our interpretation.Comment: 6 pages, 3 figure
In Utero Exposure to 2,3,7,8-Tetrachlorodibenzo-p-Dioxin Affects the Development of Reproductive System in Mouse
PURPOSE: Exposure of male reproductive organs to 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) has been reported to cause developmental changes. In this study, we evaluated the effects of in utero TCDD exposure on male reproductive development. MATERIALS AND METHODS: Pregnant C57BL/6 mice were administered a single intraperitoneal injection of TCDD (1microgram/kg) on gestation day (GD) 15. The offspring were examined in the immature stage on postnatal day (PND) 30 and in the mature stage on PND 60. The testes were examined for histological changes, androgen receptor (AR), proliferating cell nuclear antigen (PCNA) and apoptosis following the measurement of morphological changes. RESULTS: Anogenital distance (AGD) and testis weights were reduced by TCDD exposure both on PND 30 and PND 60 while body weights and length of male offspring were not affected by TCDD. The regular sperm developmental stage was impaired with TCDD treatment on PND 30. However, no difference was found between the control group and TCDD groups on PND 60. Simultaneously, the expression of AR was also reduced on PND 30, while it was increased on PND 60 compared with the control group. The expression of PCNA was decreased whereas apoptosis was not affected by TCDD both on PND 30 and PND 60. CONCLUSION: These results suggest that in utero exposure to TCDD influences the development of testes by inhibiting the expression of AR and PCNA. Moreover, the adverse effects of TCDD on male offspring reduced over timeope
Laser-Induced Linear Electron Acceleration in Free Space
Linear acceleration in free space is a topic that has been studied for over
20 years, and its ability to eventually produce high-quality, high energy
multi-particle bunches has remained a subject of great interest. Arguments can
certainly be made that such an ability is very doubtful. Nevertheless, we chose
to develop an accurate and truly predictive theoretical formalism to explore
this remote possibility in a computational experiment. The formalism includes
exact treatment of Maxwell's equations, exact relativistic treatment of the
interaction among the multiple individual particles, and exact treatment of the
interaction at near and far field. Several surprising results emerged. For
example, we find that 30 keV electrons (2.5% energy spread) can be accelerated
to 7.7 MeV (2.5% spread) and to 205 MeV (0.25% spread) using 25 mJ and 2.5 J
lasers respectively. These findings should hopefully guide and help develop
compact, high-quality, ultra-relativistic electron sources, avoiding
conventional limits imposed by material breakdown or structural constraints.Comment: Supplementary Information starts on pg 1
Terahertz-driven linear electron acceleration
The cost, size and availability of electron accelerators is dominated by the
achievable accelerating gradient. Conventional high-brightness radio-frequency
(RF) accelerating structures operate with 30-50 MeV/m gradients. Electron
accelerators driven with optical or infrared sources have demonstrated
accelerating gradients orders of magnitude above that achievable with
conventional RF structures. However, laser-driven wakefield accelerators
require intense femtosecond sources and direct laser-driven accelerators and
suffer from low bunch charge, sub-micron tolerances and sub-femtosecond timing
requirements due to the short wavelength of operation. Here, we demonstrate the
first linear acceleration of electrons with keV energy gain using
optically-generated terahertz (THz) pulses. THz-driven accelerating structures
enable high-gradient electron or proton accelerators with simple accelerating
structures, high repetition rates and significant charge per bunch. Increasing
the operational frequency of accelerators into the THz band allows for greatly
increased accelerating gradients due to reduced complications with respect to
breakdown and pulsed heating. Electric fields in the GV/m range have been
achieved in the THz frequency band using all optical methods. With recent
advances in the generation of THz pulses via optical rectification of slightly
sub-picosecond pulses, in particular improvements in conversion efficiency and
multi-cycle pulses, increasing accelerating gradients by two orders of
magnitude over conventional linear accelerators (LINACs) has become a
possibility. These ultra-compact THz accelerators with extremely short electron
bunches hold great potential to have a transformative impact for free electron
lasers, future linear particle colliders, ultra-fast electron diffraction,
x-ray science, and medical therapy with x-rays and electron beams
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