807 research outputs found
Critical Field of MGB2 : Crossover from Clean to Dirty Regimes
We have studied the upper critical field, Bc2, in poly-crystalline MgB2
samples in which disorder was varied in a controlled way to carry selectively p
and s bands from clean to dirty limit. We have found that the clean regime
survives when p bands are dirty and s bands are midway between clean and dirty.
In this framework we can explain the anomalous behaviour of Al doped samples,
in which Bc2 decreases as doping increases.Comment: 11 pages, 2 figure
The Crossover beteween Aslamazov-Larkin and Short Wavelength Fluctuations Regimes in HTS Conductivity Experiments
We present paraconductivity (AL) measurements in three different high
temperature superconductors: a melt textured sample, a
epitaxial thin film and a highly textured
tape. The crossovers between different temperature
regimes in excess conductivity have been analysed. The Lawrence-Doniach (LD)
crossover, which separates the 2D and 3D regimes, shifts from lower to higher
temperatures as the compound anisotropy decreases. Once the LD crossover is
overcome, the fluctuation conductivity of the three compounds shows the same
universal behaviour: for all the curves bend down
according to the law. This asymptotic behaviour was
theoretically predicted previously for the high temperature region where the
short wavelength fluctuations (SWF) become important.Comment: 4 pages, Revtex, 1 PostScript figure available upon request
([email protected]); submitted to Physical Review B rapid communication
Bismuth-Gold absorber for large area TES spiderweb bolometer
Large area spiderweb bolometer of about one centimetre diameter are required for matching multimode or quasi-optical cavities in microwave antenna for CMB measurements as proposed for the Large Scale Polarization Explorer balloon borne sky survey at 140, 220, 250 GHz. Possible applications at low frequencies, 40 GHz or less, in single mode are also foreseen. The main drawback of such large absorber is the achievement of an optimal trade-off among the thermal properties, like fast internal thermal diffusivity, heat capacity and milli-second recovery time and EM characteristics, like the matching impedance and EM power dissipation. In parallel with standard micropatterned gold film absorber deposited onto silicon nitride membrane, we have tested the Bismuth Gold in order to reduce the heat capacity even if with an increase of resistivity. Films of Bismuth Gold may have low resistivity under application of a proper post-production thermal cycle. We present the fabrication method of Bismuth Gold films for our microwave absorbers and the bolometer characterization at low temperature
Enhanced flux pinning in neutron irradiated MgB2
We study the effect of neutron irradiation on the critical current density Jc
of isotopically pure polycrystalline Mg11B2 samples. For fluences in the range
1017-1018 cm-2, Jc is enhanced and its dependence on magnetic field is
significantly improved: we demonstrate that, in this regime, point-like pinning
centers are effectively introduced in the system proportionally to the neutron
fluence. Instead, for larger fluences, a strong suppression of the critical
temperature accompanied by a decrease of both the upper critical field Bc2 and
Jc is found.Comment: 13 pages, 3 igure
The Impact of Climate Change on Agriculture and Health Sectors in Tanzania: A review
The impact of climate change in Tanzania is dynamic and differs among regions as they are impacted in different ways. While other regions experience normal rainfall and temperature patterns, others have continued to experience temperature extremes, severe droughts, decline in crops production coupled with food insecurity, extreme weather episodes of heavy rainfall associated with floods, loss of lives and infectious disease outbreaks. Despite the effects of climate change being recognized in the country, awareness is limited among local people, in particular the vulnerable communities. Thus, this review aims to raise awareness by giving a broader picture of impacts of climate change on agriculture and health sector. It reveals that in many parts of Tanzania, agriculture and health sectors may continue to suffer from the effects of climate change aggregated with limited awareness among communities. It is expected, that outbreaks of infectious diseases including malaria and cholera may increase as they correlate positively with high temperatures and rainfall. As a result, health problems and deaths of people, and reduced crops production will continue. Therefore, it is recommended that, the best way to overcome climate change is to invest effectively on the irrigation agriculture; and the health sector's budget should be enough to improve health care services and prepare for outbreaks of climate change sensitive diseases. Most importantly, provision of climate change awareness to the vulnerable communities must be seriously considered. About 50 peer-reviewed articles, government and International reports published between 2000 and 2017 were reviewed
Dynamical Localization in Quasi-Periodic Driven Systems
We investigate how the time dependence of the Hamiltonian determines the
occurrence of Dynamical Localization (DL) in driven quantum systems with two
incommensurate frequencies. If both frequencies are associated to impulsive
terms, DL is permanently destroyed. In this case, we show that the evolution is
similar to a decoherent case. On the other hand, if both frequencies are
associated to smooth driving functions, DL persists although on a time scale
longer than in the periodic case. When the driving function consists of a
series of pulses of duration , we show that the localization time
increases as as the impulsive limit, , is
approached. In the intermediate case, in which only one of the frequencies is
associated to an impulsive term in the Hamiltonian, a transition from a
localized to a delocalized dynamics takes place at a certain critical value of
the strength parameter. We provide an estimate for this critical value, based
on analytical considerations. We show how, in all cases, the frequency spectrum
of the dynamical response can be used to understand the global features of the
motion. All results are numerically checked.Comment: 7 pages, 5 figures included. In this version is that Subsection III.B
and Appendix A on the quasiperiodic Fermi Accelerator has been replaced by a
reference to published wor
Monopelopia caraguata (Chironomidae: Tanypodinae: Pentaneurini) and Phytotelmatocladius delarosai (Chironomidae: Orthocladiinae) : Two Phytotelmatous Chironomids Distributed from Florida to Argentina
Fil: Siri, Augusto. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología Dr. Raúl A. Ringuelet; ArgentinaFil: Donato, Mariano. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Laboratorio de Sistemática y Biología Evolutiva; Argentin
Thermal conductivity of MgB in the superconducting state
We present thermal conductivity measurements on very pure and dense bulk
samples, as indicated by residual resistivity values as low as 0.5 mW cm and
thermal conductivity values higher than 200 W/mK. In the normal state we found
that the Wiedemann Franz law, in its generalized form, works well suggesting
that phonons do not contribute to the heat transport. The thermal conductivity
in the superconducting state has been analysed by using a two-gap model. Thank
to the large gap anisotropy we were able to evaluate quantitatively intraband
scattering relaxation times of and bands, which depend on the
disorder in different way; namely, as the disorder increases, it reduces more
effectively the relaxation times of than of bands, as
suggested by a recent calculation [1].Comment: 12 pages, 5 figure
Altered syntactic abilities in first episode patients: An inner phenomenon characterizing psychosis
Background: Research has consistently shown that language abilities represent a core dimension of psychosis; however, to date, very little is known about syntactic comprehension performance in the early stages of psychosis. This study aims to compare the linguistic abilities involved in syntactic comprehension in a large group of First Episode Psychosis (FEP) patients and healthy controls (HCs). Methods: A multiple choice test of comprehension of syntax was administered to 218 FEP patients (166 non-affective FEP patients [FEP-NA] and 52 affective FEP patients [FEP-A]) and 106 HCs. All participants were asked to match a sentence they listen with one out of four vignettes on a pc screen. Only one vignette represents the stimulus target, while the others are grammatical or non-grammatical (visual) distractors. Both grammatical and non-grammatical errors and performance in different syntactic constructions were considered. Results: FEP committed greater number of errors in the majority of TCGB language domains compared to HCs. Moreover, FEP-NA patients committed significantly more non-grammatical (z = −3.2, p = 0.007), locative (z = −4.7, p < 0.001), passive-negative (z = −3.2, p = 0.02), and relative (z = −4.6, p < 0.001) errors compared to HCs as well as more passive-affirmative errors compared to both HCs (z = −4.3, p < 0.001) and FEP-A (z = 3.1, p = 0.04). Finally, we also found that both FEP-NA and FEP-A committed more grammatical (FEP-NA: z = −9.2, p < 0.001 and FEP-A: z = −4.4, p < 0.001), total (FEP-NA: z = −8.2, p < 0.001 and FEP-A: z = 3.9, p = 0.002), and active-negative (FEP-NA: z = −5.8, p < 0.001 and FEP-A: z = −3.5, p = 0.01) errors compared to HCs. Conclusions: This study shows that the access to syntactic structures is already impaired in FEP patients, especially in those with FEP-NA, ultimately suggesting that language impairments represent a core and inner feature of psychosis even at early stages
- …