5,976 research outputs found
Field sources in a Lorentz symmetry breaking scenario with a single background vector
This paper is devoted to investigating the interactions between stationary
sources of the electromagnetic field, in a model which exhibits explicit
Lorentz-symmetry breaking due to the presence of a single background vector. We
focus on physical phenomena that emerge from this kind of breaking and which
have no counterpart in Maxwell Electrodynamics
Generation of higher derivatives operators and electromagnetic wave propagation in a Lorentz-violation scenario
We study the perturbative generation of higher-derivative operators as
corrections to the photon effective action, which are originated from a Lorentz
violation background. Such corrections are obtained, at one-loop order, through
the proper-time method, using the zeta function regularization. We focus over
the lowest order corrections and investigate their influence in the propagation
of electromagnetic waves through the vacuum, in the presence of a strong,
constant magnetic field. This is a setting of experimental relevance, since it
bases active efforts to measure non linear electromagnetic effects. After
surprising cancellations of Lorentz violating corrections to the Maxwell's
equation, we show that no effects of the kind of Lorentz violation we consider
can be detected in such a context.Comment: v2: 13 pages, no figures, section IV considerably rewritten, main
results unchanged and are now obtained in a simpler way. To appear in PL
TRANSIENT KNICKPOINTS” NO LEITO DOS RIOS, SIGNIFICADO NA EVOLUÇÃO DA PAISAGEM
Neste trabalho apresenta-se uma síntese sobre a relevância dos knickpoints na estruturação do perfil longitudinal dos rios e indirectamente, na evolução da paisagem. Aborda-se o significado dos knickpoints relativamente aos conceitos de equilíbrio e desequilíbrio do perfil longitudinal, difundidos na literatura. Leis que regem a incisão fluvial, testadas em modelos físico-matemáticos, estabelecidos nas duas últimas décadas, são também referidas. Salientam-se as potencialidades que decorrem deste tipo de análise quantitativa dos perfis longitudinais dos rios, nomeadamente: a identificação de troços relíquia e troços ajustados a novas condições de equilíbrio; a reconstituição de antigos leitos (erodidos) a jusante de knickpoints transitórios e a correlação com outras unidades geomorfológicas, como sejam os terraços fluviais. A relação entre o comportamento das vagas de erosão com a morfologia dos knickpoints e com certos modelos de evolução da paisagem é salientada neste trabalho
Nutrição, calagem e adubação.
O cultivo da bananeira demanda grandes quantidades de nutrientes para manter o bom desenvolvimento da planta e boa produção, sendo que o potássio e o nitrogênio são os mais exigidos. Em ordem decrescente, a bananeira absorve os seguintes nutrientes: a) macronutrientes - potássio (K) > nitrogênio (N) > cálcio (Cal) > magnésio (Mg) > enxofre (S) > fósforo (P); e b) micronutrientes - cloro (Cl) > manganês (Mn) > ferro (Fe) > zinco (Zn) > boro (B) > cobre (Cu). Em média, um bananal retira, por tonelada de frutos, 5,2 Kg de K; 1,9 Kg de N; 0,30 Kg de Mg; 0,23 Kg de P e 0,22 Kg de Ca. A grande exigência da bananeira e os baixos teores de nutrientes em alguns solos fazem com que seu cultivo em sistemas intensivos necessite de elevado uso de fertilizantes e água, para uma maior eficiência na absorção dos nutrientes
Primary Antiphospholipid Syndrome: Pregnancy Outcome in a Portuguese Population
Introduction:Women with antiphospholipid syndrome(APS) may suffer from recurrent miscarriage, fetal death, fetal growth restriction (FGR), pre-eclampsia, placental abruption, premature delivery and thrombosis. Treatment with aspirin and
low molecular weight heparin (LMWH) combined
with close maternal-fetal surveillance can change these outcomes.
Objective: To assess maternal and perinatal outcome in a cohort of Portuguese women with primary APS.
Patients and Methods: A retrospective analysis of 51 women with primary APS followed in our institution (January 1994 to December 2007). Forty one(80.4%) had past pregnancy morbidity and 35.3%(n=18) suffered previous thrombotic events. In their past they had a total of 116 pregnancies of which
only 13.79 % resulted in live births. Forty four patients had positive anticardiolipin antibodies and 33 lupus anticoagulant. All women received treatment with low dose aspirin and LMWH.
Results: There were a total of 67 gestations (66 single and one multiple). The live birth rate was 85.1%(57/67) with 10 pregnancy failures: seven in the first and second trimesters, one late fetal death and two
medical terminations of pregnancy (one APS related).
Mean (± SD) birth weight was 2837 ± 812 g
and mean gestational age 37 ± 3.3 weeks. There were nine cases of FGR and 13 hypertensive complications(4 HELLP syndromes). 54.4% of the patients
delivered by caesarean section.
Conclusions: In our cohort, early treatment with aspirin and LMWH combined with close maternal-fetal surveillance was associated with a very high chance of a live newborn
Warfarin Hipersensitivity. How to Deal with it?
Os autores descrevem um caso clínico de hipersensibilidade à varfarina traduzido por
uma elevação acentuada do INR, aquando da introdução do fármaco em doente com
antecedentes tromboembólicos. Da pesquisa de polimorfismos para os genes VKORC1 e CYP2C9, utilizando técnicas de amplificação por PCR e hibridização reversa, apurou-se heterozigotia para -1639G>A (gene VKORC1) e homozigotia para 1075A>C (genótipo
CYP2C9*3/*3). Os autores fazem uma revisão da farmacodinâmica da varfarina e da sua
acção sobre a vitamina K, sugerindo-se indicações para a investigação de algumas variações genéticas, no sentido de obviar potenciais complicações associadas ao fármaco
Diagnosing numerical Cherenkov instabilities in relativistic plasma simulations based on general meshes
Numerical Cherenkov radiation (NCR) or instability is a detrimental effect
frequently found in electromagnetic particle-in-cell (EM-PIC) simulations
involving relativistic plasma beams. NCR is caused by spurious coupling between
electromagnetic-field modes and multiple beam resonances. This coupling may
result from the slow down of poorly-resolved waves due to numerical (grid)
dispersion and from aliasing mechanisms. NCR has been studied in the past for
finite-difference-based EM-PIC algorithms on regular (structured) meshes with
rectangular elements. In this work, we extend the analysis of NCR to
finite-element-based EM-PIC algorithms implemented on unstructured meshes. The
influence of different mesh element shapes and mesh layouts on NCR is studied.
Analytic predictions are compared against results from finite-element-based
EM-PIC simulations of relativistic plasma beams on various mesh types.Comment: 31 pages, 20 figure
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