110 research outputs found
Cathodo- and radioluminescence of Tm:YAG and Nd:YAG in an extended wavelength range
We have studied the cathodo- and radioluminescence of Nd:YAG and of Tm:YAG
single crystals in an extended wavelength range up to m in view
of developing a new kind of detector for low-energy, low-rate energy deposition
events. Whereas the light yield in the visible range is as large as photons/MeV, in good agreement with literature results, in the
infrared range we have found a light yield photons/MeV, thereby proving that ionizing radiation is particularly
efficient in populating the low lying levels of rare earth doped crystals.Comment: submitted for publication in Journal of Luminescenc
A new technique for infrared scintillation measurements
We propose a new technique to measure the infrared scintillation light yield
of rare earth (RE) doped crystals by comparing it to near UV-visible
scintillation of a calibrated Pr:(LuY)AlO
sample. As an example, we apply this technique to provide the light yield in
visible and infrared range up to \SI{1700}{nm} of this crystal.Comment: submitted to NIM
Supersymmetric AdS(4) compactifications of IIA supergravity
We derive necessary and sufficient conditions for N=1 compactifications of
(massive) IIA supergravity to AdS(4) in the language of SU(3) structures. We
find new solutions characterized by constant dilaton and nonzero fluxes for all
form fields. All fluxes are given in terms of the geometrical data of the
internal compact space. The latter is constrained to belong to a special class
of half-flat manifolds.Comment: 24 pages, references adde
Laser induced fluorescence for axion dark matter detection: a feasibility study in YLiF:Er
We present a detection scheme to search for QCD axion dark matter, that is
based on a direct interaction between axions and electrons explicitly predicted
by DFSZ axion models. The local axion dark matter field shall drive transitions
between Zeeman-split atomic levels separated by the axion rest mass energy . Axion-related excitations are then detected with an upconversion scheme
involving a pump laser that converts the absorbed axion energy (
hundreds of eV) to visible or infrared photons, where single photon
detection is an established technique. The proposed scheme involves rare-earth
ions doped into solid-state crystalline materials, and the optical transitions
take place between energy levels of electron configuration. Beyond
discussing theoretical aspects and requirements to achieve a cosmologically
relevant sensitivity, especially in terms of spectroscopic material properties,
we experimentally investigate backgrounds due to the pump laser at temperatures
in the range K. Our results rule out excitation of the upper Zeeman
component of the ground state by laser-related heating effects, and are of some
help in optimizing activated material parameters to suppress the
multiphonon-assisted Stokes fluorescence.Comment: 8 pages, 5 figure
Particle detection through the quantum counter concept in YAG:Er
We report about a novel scheme for particle detection based on the infrared
quantum counter concept. Its operation consists of a two-step excitation
process of a four level system, that can be realized in rare earth-doped
crystals when a cw pump laser is tuned to the transition from the second to the
fourth level. The incident particle raises the atoms of the active material
into a low lying, metastable energy state, triggering the absorption of the
pump laser to a higher level. Following a rapid non-radiative decay to a
fluorescent level, an optical signal is observed with a conventional detectors.
In order to demonstrate the feasibility of such a scheme, we have investigated
the emission from the fluorescent level S (540 nm band) in an
Er-doped YAG crystal pumped by a tunable titanium sapphire laser when it
is irradiated with 60 keV electrons delivered by an electron gun. We have
obtained a clear signature this excitation increases the
metastable level population that can efficiently be exploited to generate a
detectable optical signal
A study of childhood febrile convulsions with particular reference to HHV-6 infection: Pathogenic considerations
Most febrile convulsions (FC) in infants occur during a viral infection, particularly in children of less than 3 years of age: human herpesvirus 6 (HHV-6) has an Important pathogenic role. To evaluate the link between this and other viruses and FC, a group of 65 children (mean age 18.46 months: SD+/-9.19) with a first episode of simple FC (G1) was compared with 24 children (mean age 19.29 months, SD+/-13.17) with a febrile syndrome but without FC (G2). Virological study showed the following infections: HHV-6 in 23/65 of G1 and in 12/24 of G2, adenoviruses (ADV) in 9/65 of G1 and in 0/24, of G2, syncytial respiratory virus (SRV) in 3/28 of G1 and in 0/2 of G2. HSV-1 in 6/65 of G1 and in 1/24 of G2, cytomegalovirus (CMV in 2/65 of G1 and in 0/24 of G2 and HHV-7 in 1/42 of GI and in 1/13 of G2. Children in G1, statistically compared with G2, were significantly more Likely to have a family history of FC and circulating granulocytes, while IgM and alpha 2-globulin were less probable. Some cytokines (IL 1 beta, TNF beta and GM-CSF) were found in 24 children in G1 and 12 in G2; no differences were found between the two groups. In the light of our data and of the recent literature, the possibility that the cytokines may act on the nervous system cannot be excluded. Among the HHV-6-infected children, those suf fering from convulsions were statistically more likely to have a family history of FC and ISM, while IgA were less likely. In G1, 57 cases were followed up over 2 years: 9 of them had a second episode of FC. Virological diagnosis at the first episode of FC revealed HHV-6 infection in 3 cases, 2 of these being due to viral reactivation. We underline the important role of HHV-6 infection in FC and postulate a relation ship between family history and the immunity of the patient; this is confirmed by the loss of statistical significance in the reduction of IgM in G1 compared with G2 with no family history of FC. The reactivation of FC by HHV-6 is a possibility to be borne in mind, an increased number of cases would be needed to confirm this hypothesis
AdS Strings with Torsion: Non-complex Heterotic Compactifications
Combining the effects of fluxes and gaugino condensation in heterotic
supergravity, we use a ten-dimensional approach to find a new class of
four-dimensional supersymmetric AdS compactifications on almost-Hermitian
manifolds of SU(3) structure. Computation of the torsion allows a
classification of the internal geometry, which for a particular combination of
fluxes and condensate, is nearly Kahler. We argue that all moduli are fixed,
and we show that the Kahler potential and superpotential proposed in the
literature yield the correct AdS radius. In the nearly Kahler case, we are able
to solve the H Bianchi using a nonstandard embedding. Finally, we point out
subtleties in deriving the effective superpotential and understanding the
heterotic supergravity in the presence of a gaugino condensate.Comment: 42 pages; v2. added refs, revised discussion of Bianchi for N
Complete Calabi-Yau metrics from Kahler metrics in D=4
In the present work the local form of certain Calabi-Yau metrics possessing a
local Hamiltonian Killing vector is described in terms of a single non linear
equation. The main assumptions are that the complex -form is of the form
, where is preserved by the Killing
vector, and that the space of the orbits of the Killing vector is, for fixed
value of the momentum map coordinate, a complex 4-manifold, in such a way that
the complex structure of the 4-manifold is part of the complex structure of the
complex 3-fold. The link with the solution generating techniques of [26]-[28]
is made explicit and in particular an example with holonomy exactly SU(3) is
found by use of the linearization of [26], which was found in the context of D6
branes wrapping a holomorphic 1-fold in a hyperkahler manifold. But the main
improvement of the present method, unlike the ones presented in [26]-[28], does
not rely in an initial hyperkahler structure. Additionally the complications
when dealing with non linear operators over the curved hyperkahler space are
avoided by use of this method.Comment: Version accepted for publication in Phys.Rev.
New non compact Calabi-Yau metrics in D=6
A method for constructing explicit Calabi-Yau metrics in six dimensions in
terms of an initial hyperkahler structure is presented. The equations to solve
are non linear in general, but become linear when the objects describing the
metric depend on only one complex coordinate of the hyperkahler 4-dimensional
space and its complex conjugated. This situation in particular gives a dual
description of D6-branes wrapping a complex 1-cycle inside the hyperkahler
space, which was studied by Fayyazuddin. The present work generalize the
construction given by him. But the explicit solutions we present correspond to
the non linear problem. This is a non linear equation with respect to two
variables which, with the help of some specific anzatz, is reduced to a non
linear equation with a single variable solvable in terms of elliptic functions.
In these terms we construct an infinite family of non compact Calabi-Yau
metrics.Comment: A numerical error has been corrected together with the corresponding
analysis of the metri
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