Extra dimensions, orthopositronium decay, and stellar cooling

In a class of extra dimensional models with a warped metric and a single brane the photon can be localized on the brane by gravity only. An intriguing feature of these models is the possibility of the photon escaping into the extra dimensions. The search for this effect has motivated the present round of precision orthopositronium decay experiments. We point out that in this framework a photon in plasma should be metastable. We consider the astrophysical consequences of this observation, in particular, what it implies for the plasmon decay rate in globular cluster stars and for the core-collapse supernova cooling rate. The resulting bounds on the model parameter exceed the possible reach of orthopositronium experiments by many orders of magnitude.Comment: 13 pages, no figure

Stellar Recipes for Axion Hunters

There are a number of observational hints from astrophysics which point to the existence of stellar energy losses beyond the ones accounted for by neutrino emission. These excessive energy losses may be explained by the existence of a new sub-keV mass pseudoscalar Nambu--Goldstone boson with tiny couplings to photons, electrons, and nucleons. An attractive possibility is to identify this particle with the axion -- the hypothetical pseudo Nambu--Goldstone boson predicted by the Peccei--Quinn solution to the strong CP problem. We explore this possibility in terms of a DFSZ-type axion and of a KSVZ-type axion/majoron, respectively. Both models allow a good global fit to the data, prefering an axion mass around 10 meV. We show that future axion experiments -- the fifth force experiment ARIADNE and the helioscope IAXO -- can attack the preferred mass range from the lower and higher end, respectively. An axion in this mass range can also be the main constituent of dark matter.Comment: 32 pages, 5 figure

Nucleon-Nucleon Bremsstrahlung emission of massive Axion

We consider the problem of axion production by bremsstrahlung emission in a nuclear medium. The usual assumption of a massless axion is replaced by more general hypotheses, so that we can describe the emission process for axions with mass up to a few MeV. We point out that in certain physical situations the contribution from non-zero mass is non-negligible. In particular, in the mechanism for the production of Gamma Ray Bursts via emission of heavy axions the axion mass m_a ~ 1MeV is comparable with the temperature of the nuclear medium and thus can not be disregarded. Looking at our results we find, in fact, a fairly considerable reduction of the axion luminosity in that mechanism.Comment: 16 pages, 5 figure

ADOLESCENT BRAIN ON COCAINE: SHORT- AND LONG-TERM MOLECULAR CHANGES FOLLOWING REPEATED PSYCHOSTIMULANT EXPOSURE

Drug addiction is a chronic, relapsing brain disorder that relies on the substantial shift from a controlled drug use to compulsive drug seeking despite negative consequences. Among the growing and broad field of illicit drugs, so far cocaine still represents the most used psychostimulant. Although drug addiction can be considered an adult brain disorder, drug use peaks during adolescence. During this period the brain undergoes profound structural and molecular changes, making the adolescent brain more vulnerable to the pharmacological effects brought about by drugs of abuse and, perhaps, may set the stage to initiate drug use or relapse to drugs of abuse later in life. Accordingly, to understand the molecular mechanisms underlying drug use in adults is necessary to investigate the drug-induced molecular changes in the adolescent brain. We focused our molecular analyses on the medial prefrontal cortex (mPFC), a brain region that is still developing during adolescence and may result more sensitive to the pharmacologic effects of cocaine. We found that repeated exposure to cocaine during adolescence induces a maladaptive neuroplasticity after either short- and long-term withdrawal. In particular, we found that short-term withdrawal from developmental exposure to cocaine alters the physiological response of the glutamatergic system to a challenging situation, thus generating a hyper-reactive glutamatergic synapse. Moreover, three days of withdrawal are sufficient to induce a pro-depressive behavior that, perhaps, may reflect the cocaine-induced alteration of the stress-related system in the mPFC. One of the major clinical issues of drug addiction is the relapse even after long periods of abstinence. Accordingly, we investigated whether long-term withdrawal from developmental exposure to cocaine may have altered markers of neuroplasticity in the mPFC. Interestingly, we found an increase BDNF expression, its high-affinity receptor TrkB and the associated signaling pathway. On the other hand, we found reduced expression of GluA1 subunit of AMPA receptors, suggesting, perhaps, an indirect effect of BDNF on the glutamatergic system through the up-regulation of ARC expression. Further, we found that long-term withdrawal from developmental exposure to cocaine increases FGF-2 expression in the mPFC, as observed for BDNF. Taking into account that adolescence is a vulnerable period to initiate drug use, we investigated whether a single injection of cocaine is sufficient to produce a maladaptive molecular background that may contribute to develop maladaptive behaviors. Interestingly, we found that a single injection to cocaine is sufficient to up-regulate FGF-2 expression in the mPFC seven days later while its expression returns to baseline after the second challenge. However, a different modulation of the neurotrophin was observed in hippocampus. In particular, a single injection of cocaine reduces FGF-2 expression, as well as ARC, seven days later, suggesting, at least in part, a reduced neuronal activity. Altogether, these results further highlight the adolescence as a period of high vulnerability to the pharmacological effects brought about by cocaine in the mPFC after a single injection rather than repeated exposure to the psychostimulant. Further, these results add important preclinical evidence to the short- or long-term action of cocaine following exposure during adolescence

LIMB BODY WALL COMPLEX IN TWO HETEROZYGOTIC TWINS: A CASE REPORT

Introdution. Limb-Body Wall Complex (LBWC) is a congenital defect which includes at least two of the following characteristics: abdominal and/or thoracic body wall defects, exencephaly or encephalocoele with or without craniofacial defects (56%) and spinal defects associated with marked vertebral or sacral defects (95%). Case Report. We present a case report of an infant with LBWC, borned by diamniotic twin pregnancy. A prenatal ultrasound reported an healthy fetus and a fetus with multiple malformations. At birth we found a big abdominal wall defect, absence of scrotal sac and testicles, asymmetric chest and no major deformities in craniofacial region. At 2 hours of life, we removed the amniotic sac, we put the stomach and the spleen in the abdominal cavity, which is virtual, and positioned a spring-loaded silo. At 15th day of life we had complete reduction of the intestinal loops and liver and we closed the wall defect with a prosthesis and a cryopreserved skin. The general conditions of the patient, very severe since birth, became progressively worse and he died in the 21st day of life. Discussion. Once the diagnosis is done the physician should offer the parents a therapeutic abortion, and above all, in case they want to carry the pregnancy to term, we need to prepare them to the severity of the malformation and the high probability of death

Magnetic Helicity Generation from the Cosmic Axion Field

The coupling between a primordial magnetic field and the cosmic axion field generates a helical component of the magnetic field around the time in which the axion starts to oscillate. If the energy density of the seed magnetic field is comparable to the energy density of the universe at that time, then the resulting magnetic helicity is about |H_B| \simeq (10^{-20} G)^2 kpc and remains constant after its generation. As a corollary, we find that the standard properties of the oscillating axion remain unchanged even in the presence of very strong magnetic fields.Comment: 6 pages, 2 figures. Accepted for publication in Phys. Rev. D. Minor revisions and new references adde

Intracavity intensity noise suppression in the inverse Compton scattering source BriXSinO exploiting carrier-envelope offset manipulation

We report on a technique that exploits the control of the carrier -envelope offset to suppress the frequency-to-intensity noise conversion in the locking of a mode-locking laser against a high-finesse optical enhancement resonator. A proper combination of the laser carrier-envelope offset and the resonator finesse allows the improvement of the signal-to-noise ratio of the optical intensity trapped into the optical resonator. In this paper, we show the application of this technique in the laser system of the inverse Compton scattering source BriXSinO, currently under development in Milan, Italy, demonstrating the possibility of achieving an intracavity intensity noise reduction of a factor of 20

Origin and destination attachment: study of cultural integration on Twitter

The cultural integration of immigrants conditions their overall socio-economic integration as well as natives’ attitudes towards globalisation in general and immigration in particular. At the same time, excessive integration—or assimilation—can be detrimental in that it implies forfeiting one’s ties to the origin country and eventually translates into a loss of diversity (from the viewpoint of host countries) and of global connections (from the viewpoint of both host and home countries). Cultural integration can be described using two dimensions: the preservation of links to the origin country and culture, which we call origin attachment, and the creation of new links together with the adoption of cultural traits from the new residence country, which we call destination attachment. In this paper we introduce a means to quantify these two aspects based on Twitter data. We build origin and destination attachment indices and analyse their possible determinants (e.g., language proximity, distance between countries), also in relation to Hofstede’s cultural dimension scores. The results stress the importance of language: a common language between origin and destination countries favours origin attachment, as does low proficiency in the host language. Common geographical borders seem to favour both origin and destination attachment. Regarding cultural dimensions, larger differences among origin and destination countries in terms of Individualism, Masculinity and Uncertainty appear to favour destination attachment and lower origin attachment

A Note on the Cosmic Evolution of the Axion in a Strong Magnetic Field

It has been pointed out in the literature that in the presence of an external magnetic field the axion mass receives an electromagnetic contribution. We show that if a magnetic field with energy density larger than ~10^{-8} times the energy density of the Universe existed at temperatures of a few GeV, that contribution would be dominant and consequently the cosmic evolution of the axion field would change substantially. In particular, the expected axion relic abundance would be lowered, allowing a small relaxation of the present cosmological bound on the Peccei-Quinn constant.Comment: 2 pages, no figures. Minor changes. References added. Accepted for publication in JCA