19,404 research outputs found
Influence of surface passivation on ultrafast carrier dynamics and terahertz radiation generation in GaAs
The carrier dynamics of photoexcited electrons in the vicinity of the surface
of (NH4)2S-passivated GaAs were studied via terahertz (THz) emission
spectroscopy and optical-pump THz-probe spectroscopy. THz emission spectroscopy
measurements, coupled with Monte Carlo simulations of THz emission, revealed
that the surface electric field of GaAs reverses after passivation. The
conductivity of photoexcited electrons was determined via optical-pump
THz-probe spectroscopy, and was found to double after passivation. These
experiments demonstrate that passivation significantly reduces the surface
state density and surface recombination velocity of GaAs. Finally, we have
demonstrated that passivation leads to an enhancement in the power radiated by
photoconductive switch THz emitters, thereby showing the important influence of
surface chemistry on the performance of ultrafast THz photonic devices.Comment: 4 pages, 3 figures, to appear in Applied Physics Letter
A quantum-mechanical Maxwell's demon
A Maxwell's demon is a device that gets information and trades it in for
thermodynamic advantage, in apparent (but not actual) contradiction to the
second law of thermodynamics. Quantum-mechanical versions of Maxwell's demon
exhibit features that classical versions do not: in particular, a device that
gets information about a quantum system disturbs it in the process. In
addition, the information produced by quantum measurement acts as an additional
source of thermodynamic inefficiency. This paper investigates the properties of
quantum-mechanical Maxwell's demons, and proposes experimentally realizable
models of such devices.Comment: 13 pages, Te
Study of 'ratio' automatically assembled structures final report, 15 jun. 1963 - 15 jun. 1964
Structural analysis of RATIO automatically assembled panel sections for application to spaceborne paraboloidal antenn
Polarisation-sensitive terahertz detection by multicontact photoconductive receivers
We have developed a terahertz radiation detector that measures both the
amplitude and polarization of the electric field as a function of time. The
device is a three-contact photoconductive receiver designed so that two
orthogonal electric-field components of an arbitrary polarized electromagnetic
wave may be detected simultaneously. The detector was fabricated on Fe+
ion-implanted InP. Polarization-sensitive detection is demonstrated with an
extinction ratio better than 100:1. This type of device will have immediate
application in studies of birefringent and optically active materials in the
far-infrared region of the spectrum.Comment: 3 pages, 3 figure
The economy of mule production in the South and methods of management
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ANION EXCHANGE SEPARATION OF TRIVALENT ACTINIDES AND LANTHANIDES
A process for separating americium and curium from rare earths by anion exchange based on selective chloride complexing was developed and tested on a laboratory scale. The separation is accomplished by sorption of americium, curium, and rare earths on Dowex 1-10X resin from a solution of 8 M LiNO/dub 3/ followed by selective elution of rare earths with 10 M LiCl and americium-curium elution with 1 M LiCl. In a laboratory demonstration of this process, greater than 99.5% of americium tracer containing no detectable amounts of rare earths was recovered. (auth
Multiple Keratoacanthomas, Philadelphia Chromosome+ Acute Lymphoblastic Leukemia, and Dasatinib: A Case Report
Background: Treatment for adult Philadelphia chromosome+ acute lymphoblastic leukemia includes using dasatinib, a tyrosine kinase inhibitor. Cutaneous squamous cell carcinomas and keratoacanthomas are common findings in patients treated with BRAF inhibitors of tyrosine kinases. No documentation of dasatinib inducing multiple keratoacanthomas, squamous cell carcinomas type during treatment of Philadelphia chromosome+ acute lymphoblastic leukemia is currently available. Case: A 77-year-old Caucasian male presented to the dermatology clinic two months after starting treatment with dasatinib for Philadelphia chromosome positive+ acute lymphoblastic leukemia. Biopsies confirmed the lesions on the arms, chest, legs and back as keratoacanthoma (KA) type of squamous cell carcinomas (SCCs). The cutaneous lesions were surgically removed and no new or recurrent lesions were detected since their initial rapid onset despite continued dasatinib therapy. Conclusion: This report of the rapid onset of keratoacanthoma type squamous cell carcinomas in a patient with Philadelphia chromosome+ acute lymphoblastic leukemia treated with dasatinib is presumed to be the first due to the rarity of adult Philadelphia chromosome+ acute lymphoblastic leukemia. This report documents another tyrosine kinase inhibitor that is associated with the eruption of keratoacanthomas, and adds to the literature regarding the regularity of this relatively common side effect, which may have treatment other than surgery if only a few lesions are present
Charge trapping in polymer transistors probed by terahertz spectroscopy and scanning probe potentiometry
Terahertz time-domain spectroscopy and scanning probe potentiometry were used
to investigate charge trapping in polymer field-effect transistors fabricated
on a silicon gate. The hole density in the transistor channel was determined
from the reduction in the transmitted terahertz radiation under an applied gate
voltage. Prolonged device operation creates an exponential decay in the
differential terahertz transmission, compatible with an increase in the density
of trapped holes in the polymer channel. Taken in combination with scanning
probe potentionmetry measurements, these results indicate that device
degradation is largely a consequence of hole trapping, rather than of changes
to the mobility of free holes in the polymer.Comment: 4 pages, 3 figure
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