8,809 research outputs found
Intense, carrier frequency and bandwidth tunable quasi single-cycle pulses from an organic emitter covering the Terahertz frequency gap
In Terahertz (THz) science, one of the long-standing challenges has been the formation of spectrally dense, single-cycle pulses with tunable duration and spectrum across the frequency range of 0.1-15 THz (THz gap). This frequency band, lying between the electronically and optically accessible spectra hosts important molecular fingerprints and collective modes which cannot be fully controlled by present strong-field THz sources. We present a method that provides powerful single-cycle THz pulses in the THz gap with a stable absolute phase whose duration can be continuously selected between 68 fs and 1100 fs. The loss-free and chirp-free technique is based on optical rectification of a wavelength-tunable pump pulse in the organic emitter HMQ-TMS that allows for tuning of the spectral bandwidth from 1 to more than 7 octaves over the entire THz gap. The presented source tunability of the temporal carrier frequency and spectrum expands the scope of spectrally dense THz sources to time-resolved nonlinear THz spectroscopy in the entire THz gap. This opens new opportunities towards ultrafast coherent control over matter and light
a follow-up on bone graft stability and implant success
Background Until now, sinus floor elevation represents the gold standard
procedure in the atrophic maxilla in order to facilitate dental implant
insertion. Although the procedure remains highly predictive, the perforation
of the Schneiderian membrane might compromise the stability of the augmented
bone and implant success due to chronic sinus infection. The aim of this
retrospective cohort study was to show that a membrane tear, if detected and
surgically properly addressed, has no influence on the survival of dental
implants and bone resorption in the augmented area. Methods Thirty-one
patients with 39 perforations could be included in this evaluation, and a
control group of 32 patients with 40 sinus lift procedures without
complications were compared regarding the radiographically determined
development of bone level, peri-implant infection, and implant loss. Results
Implant survival was 98.9% in the perforation group over an observation period
of 2.7 (± 2.03) years compared to 100% in the control group after 1.8 (± 1.57)
years. The residual bone level was significantly lower in the perforation
group (p = 0.05) but showed no difference direct postoperatively (p = 0.7851)
or in the follow-up assessment (p = 0.2338). Bone resorption remained not
different between both groups (p = 0.945). A two-stage procedure was more
frequent in the perforation group (p = 0.0003) as well as peri-implantitis (p
= 0.0004). Conclusions Within the limits of our study, the perforation of the
Schneiderian membrane did not have a negative impact on long-term graft
stability or the overall implant survival
Cost risk benefit analysis to support chemoprophylaxis policy for travellers to malaria endemic countries
BACKGROUND: In a number of malaria endemic regions, tourists and travellers face a declining risk of travel associated malaria, in part due to successful malaria control. Many millions of visitors to these regions are recommended, via national and international policy, to use chemoprophylaxis which has a well recognized morbidity profile. To evaluate whether current malaria chemo-prophylactic policy for travellers is cost effective when adjusted for endemic transmission risk and duration of exposure. a framework, based on partial cost-benefit analysis was used. METHODS: Using a three component model combining a probability component, a cost component and a malaria risk component, the study estimated health costs avoided through use of chemoprophylaxis and costs of disease prevention (including adverse events and pre-travel advice for visits to five popular high and low malaria endemic regions) and malaria transmission risk using imported malaria cases and numbers of travellers to malarious countries. By calculating the minimal threshold malaria risk below which the economic costs of chemoprophylaxis are greater than the avoided health costs we were able to identify the point at which chemoprophylaxis would be economically rational. RESULTS: The threshold incidence at which malaria chemoprophylaxis policy becomes cost effective for UK travellers is an accumulated risk of 1.13% assuming a given set of cost parameters. The period a travellers need to remain exposed to achieve this accumulated risk varied from 30 to more than 365 days, depending on the regions intensity of malaria transmission. CONCLUSIONS: The cost-benefit analysis identified that chemoprophylaxis use was not a cost-effective policy for travellers to Thailand or the Amazon region of Brazil, but was cost-effective for travel to West Africa and for those staying longer than 45 days in India and Indonesia
Heterogeneous Catalysis under pressure - In-situ neutron diffraction under industrial conditions
The present work describes the application of a tubular reactor that allows in-situ neutron diffraction on working catalysts at high pressures. The designed reactor enables the application to a sample of industrially-relevant reaction conditions, i.e., in a temperature range up to 330° C and 60 bar pressure, coupled with online gas-analysis. Application of the cell is demonstrated by ammonia synthesis over a commercial catalyst with diffraction data obtained from the high-resolution powder diffractometer, Echidna, at the Australian Nuclear Science and Technology Organisation, ANSTO
Weak Long-Ranged Casimir Attraction in Colloidal Crystals
We investigate the influence of geometric confinement on the free energy of
an idealized model for charge-stabilized colloidal suspensions. The mean-field
Poisson-Boltzmann formulation for this system predicts pure repulsion among
macroionic colloidal spheres. Fluctuations in the simple ions' distribution
provide a mechanism for the macroions to attract each other at large
separations. Although this Casimir interaction is long-ranged, it is too weak
to influence colloidal crystals' dynamics.Comment: 5 pages 2 figures ReVTe
Fuzzy Fibers: Uncertainty in dMRI Tractography
Fiber tracking based on diffusion weighted Magnetic Resonance Imaging (dMRI)
allows for noninvasive reconstruction of fiber bundles in the human brain. In
this chapter, we discuss sources of error and uncertainty in this technique,
and review strategies that afford a more reliable interpretation of the
results. This includes methods for computing and rendering probabilistic
tractograms, which estimate precision in the face of measurement noise and
artifacts. However, we also address aspects that have received less attention
so far, such as model selection, partial voluming, and the impact of
parameters, both in preprocessing and in fiber tracking itself. We conclude by
giving impulses for future research
Possible large direct CP asymmetry in hadronic B+- -> \pi+- \eta' decays
We calculate the branching ratio and direct CP asymmetry in nonleptonic two
body B decays B^+- ->\pi^+- \eta'. It is shown that the tree diagram and gluon
fusion mechanism via penguin diagram have comparable contributions to these
decays which, as a result, could provide an interesting venue for investigating
CP violation. Our estimate shows that the direct CP asymmetry in the above
decays could be as large as 75% which along with a branching ratio B(B^-
->\pi^- \eta')=3.4 X 10^{-6} should be accessible to experiment in the near
future.Comment: 13 pages, Revtex, 4 figures (included
1/m_Q Corrections to the Heavy-to-Light-Vector Transitions in the HQET
Within the HQET, the heavy to light vector meson transitions are
systematically analyzed to the order of 1/m_Q. Besides the four universal
functions at the leading order, there are twenty-two independent universal form
factors at the order of 1/m_Q. Both the semileptonic decay B->\rho which is
relevant to the |V_{ub}| extraction, and the penguin induced decay B -> K^*
which is important to new physics discovering, depend on these form factors.
Phenomenological implications are discussed.Comment: RevTeX, 9 pages, no figure
Positron-neutrino correlation in the 0^+ \to 0^+ decay of ^{32}Ar
The positron-neutrino correlation in the decay of
Ar was measured at ISOLDE by analyzing the effect of lepton recoil on
the shape of the narrow proton group following the superallowed decay. Our
result is consistent with the Standard Model prediction. For vanishing Fierz
interference we find , which yields improved
constraints on scalar weak interactions
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