6,650 research outputs found
Making precise predictions of the Casimir force between metallic plates via a weighted Kramers-Kronig transform
The possibility of making precise predictions for the Casimir force is
essential for the theoretical interpretation of current precision experiments
on the thermal Casimir effect with metallic plates, especially for sub-micron
separations. For this purpose it is necessary to estimate very accurately the
dielectric function of a conductor along the imaginary frequency axis. This
task is complicated in the case of ohmic conductors, because optical data do
not usually extend to sufficiently low frequencies to permit an accurate
evaluation of the standard Kramers-Kronig integral used to compute . By making important improvements in the results of a previous paper by
the author, it is shown that this difficulty can be resolved by considering
suitable weighted dispersions relations, which strongly suppress the
contribution of low frequencies. The weighted dispersion formulae presented in
this paper permit to estimate accurately the dielectric function of ohmic
conductors for imaginary frequencies, on the basis of optical data extending
from the IR to the UV, with no need of uncontrolled data extrapolations towards
zero frequency that are instead necessary with standard Kramers-Kronig
relations. Applications to several sets of data for gold films are presented to
demonstrate viability of the new dispersion formulae.Comment: 18 pages, 15 encapsulated figures. In the revised version important
improvements have been made, which affect the main conclusions of the pape
Sensitive survey for 13CO, CN, H2CO, and SO in the disks of T Tauri and Herbig Ae stars II: Stars in Oph and upper Scorpius
We attempt to determine the molecular composition of disks around young
low-mass stars in the Oph region and to compare our results with a
similar study performed in the Taurus-Auriga region. We used the IRAM 30 m
telescope to perform a sensitive search for CN N=2-1 in 29 T Tauri stars
located in the Oph and upper Scorpius regions. CO J=2-1 is
observed simultaneously to provide an indication of the level of confusion with
the surrounding molecular cloud. The bandpass also contains two transitions of
ortho-HCO, one of SO, and the CO J=2-1 line, which provides
complementary information on the nature of the emission. Contamination by
molecular cloud in CO and even CO is ubiquitous. The CN detection
rate appears to be lower than for the Taurus region, with only four sources
being detected (three are attributable to disks). HCO emission is found
more frequently, but appears in general to be due to the surrounding cloud. The
weaker emission than in Taurus may suggest that the average disk size in the
Oph region is smaller than in the Taurus cloud. Chemical modeling shows
that the somewhat higher expected disk temperatures in Oph play a direct
role in decreasing the CN abundance. Warmer dust temperatures contribute to
convert CN into less volatile forms. In such a young region, CN is no longer a
simple, sensitive tracer of disks, and observations with other tracers and at
high enough resolution with ALMA are required to probe the gas disk population.Comment: 18 pages, 5 figures, accepted for publication in A&
Dynamical Masses of Low Mass Stars in the Taurus and Ophiuchus Star Forming Regions
We report new dynamical masses for 5 pre-main sequence (PMS) stars in the
L1495 region of the Taurus star-forming region (SFR) and 6 in the L1688 region
of the Ophiuchus SFR. Since these regions have VLBA parallaxes these are
absolute measurements of the stars' masses and are independent of their
effective temperatures and luminosities. Seven of the stars have masses
solar masses, thus providing data in a mass range with little data, and of
these, 6 are measured to precision . We find 8 stars with masses in the
range 0.09 to 1.1 solar mass that agree well with the current generation of PMS
evolutionary models. The ages of the stars we measured in the Taurus SFR are in
the range 1-3 MY, and MY for those in L1688. We also measured the
dynamical masses of 14 stars in the ALMA archival data for Akeson~\&~Jensen's
Cycle 0 project on binaries in the Taurus SFR. We find that the masses of 7 of
the targets are so large that they cannot be reconciled with reported values of
their luminosity and effective temperature. We suggest that these targets are
themselves binaries or triples.Comment: 20 page
Fuel-Responsive Allosteric DNA-Based Aptamers for the Transient Release of ATP and Cocaine
We show herein that allostery offers a key strategy for the design of out-of-equilibrium systems by engineering allosteric DNA-based nanodevices for the transient loading and release of small organic molecules. To demonstrate the generality of our approach, we used two model DNA-based aptamers that bind ATP and cocaine through a target-induced conformational change. We re-engineered these aptamers so that their affinity towards their specific target is controlled by a DNA sequence acting as an allosteric inhibitor. The use of an enzyme that specifically cleaves the inhibitor only when it is bound to the aptamer generates a transient allosteric control that leads to the release of ATP or cocaine from the aptamers. Our approach confirms that the programmability and predictability of nucleic acids make synthetic DNA/RNA the perfect candidate material to re-engineer synthetic receptors that can undergo chemical fuel-triggered release of small-molecule cargoes and to rationally design non-equilibrium systems
Role of Quantum Confinement in Luminescence Efficiency of Group IV Nanostructures
Experimental results obtained previously for the photoluminescence efficiency
(PL) of Ge quantum dots (QDs) are theoretically studied. A
- plot of PL versus QD diameter () resulted in an
identical slope for each Ge QD sample only when . We
identified that above 6.2 nm: due to a changing
effective mass (EM), while below 4.6 nm: due to
electron/ hole confinement. We propose that as the QD size is initially
reduced, the EM is reduced, which increases the Bohr radius and interface
scattering until eventually pure quantum confinement effects dominate at small
Quantum Limit in a Parallel Magnetic Field in Layered Conductors
We show that electron wave functions in a quasi-two-dimensional conductor in
a parallel magnetic field are always localized on conducting layers. Wave
functions and electron spectrum in a quantum limit, where the "sizes" of
quasi-classical electron orbits are of the order of nano-scale distances
between the layers, are determined. AC infrared measurements to investigate
Fermi surfaces and to test Fermi liquid theory in Q2D organic and high-Tc
materials in high magnetic fields, H = 10-45 T, are suggested.Comment: 9 pages, 2 figures; Submitted to Physical Review Letter
Laser surgery of early glottic cancer in elderly
Aim of this retrospective study is to evaluate the impact of transoral laser surgery of early glottic cancer in elderly patients in terms of
feasibility, disease-free survival, overall survival and organ preservation, in a single Institute (European Institute of Oncology). A total of
122 patients (male/female ratio 113/9), over 70s with untreated early stage glottic cancer, were consecutively evaluated and treated at the
European Institute of Oncology from 2000 to 2008. None had contraindications to general anaesthesia and all patients signed informed
consent to this surgical treatment. The severity of pre-operative comorbidities and the intra-operative risk were evaluated according to
the American Society of Anaesthesiologists Grading classification. All patients underwent laser cordectomies according to the European
Laryngological Society classification. Histopathological examination demonstrated no evidence of tumour (pT0) in 19 patients (calculated
only in patients with a previous vocal cord biopsy positive for squamous cell carcinoma), pTis in 18, pT1a in 53, pT1b in 16, pT2 in 14 and
pT3 in 2, respectively. A 10-year overall survival, a tumour specific survival and a laryngeal tumour-specific survival were, respectively,
64.9%, 84.8% and 94.3%. In conclusion, transoral laser surgery is feasible in elderly patients with early stage glottic cancer, providing
good results in terms of disease-free survival, organ preservation and quality of life. Our group of elderly patients had no intra-operative or
post-surgical complications and resumed normal activities the day after discharge from hospital. Considering these factors, we can assess,
that transoral laser surgery, therefore, represents a modern treatment that should be offered as an alternative to conventional radiotherapy in
elderly patients with early glottic cancer referred to medical centres with expertise for this surgical procedure
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