Above Barrier Dirac Multiple Scattering and Resonances

We extend an above barrier analysis made with the Schrodinger equation to the Dirac equation. We demonstrate the perfect agreement between the barrier results and back to back steps. This implies the existence of multiple (indeed infinite) reflected and transmitted wave packets. These packets may be well separated in space or partially overlap. In the latter case interference effects can occur. For the extreme case of total overlap we encounter resonances. The conditions under which resonance phenomena can be observed is discussed and illustrated by numerical calculations.Comment: 12 pages, 1 figur

The course of pregnancy and delivery in a patient with malaria

Malaria is one of the most common lethal parasitic diseases. Infection is transmitted when an infected female mosquito bites a human introducing the sporozoites into human blood. The article presents the course of pregnancy and delivery in a patient complicated by Plasmodium infection. The patient had repetitive several trips to Tanzania over a short time period before she developed the condition. She had been taking antimalarial medication (proguanil-atovaquone) in a prophylactic dose during and after her first travel to Tanzania. Following her first return to Poland she experienced infection-related symptoms

Diagnostic and therapeutic problems in the obese patient with hypothyroidism

Istnieje wiele przyczyn niedoczynności gruczołu tarczowego. Najczęściej spotykamy się jednak z autoimmunologicznym zapaleniem tarczycy. Niedoczynność pierwotna — spowodowana uszkodzeniem gruczołu tarczowego, wywołanym pr zez zapalenia tarczycy, w tym autoim - munologiczne, wycięcie tarczycy, po leczeniu jodem promieniotwórczym bądź radioterapii, nadmierną podaż jodu lub jego niedobór , niedoczynność polekową, wrodzoną niedoczyn - ność tarczycy, defekty enzymatyczne syntezy hor monów tarczycy lub obwodowa opor ność na hormony tarczycy. Niedoczynność wtórna — niedobór tyreotropiny (TSH). Niedoczynność trzeciorzędowa — niedobór tyreoliber yny (TRH) spowodowany pr zez guzy podwzgór za lub okolicy albo urazy głowy z przerwaniem ciągłości szypuły przysadki. Niedoczynność tarczycy, niezależnie od etiologii, może dawać wiele różnych objawów. Mogą one występować w różnych konfiguracjach i w różnym natężeniu. Zwykle, im cięższa niedoczynność, tym więcej objawów i tym mocniej są one wyrażone. Stosunkowo niewielkim zmianom stężeń hor monów tarczycy towar zyszą dużo wyraźniejsze zmiany w stężeniu TSH. To tłumaczy, dlaczego wzrost stężenia TSH ujawnia się szybciej i na wcześniejszych etapach niedoczynności tarczycy niż zmiany fT4 i fT3. Chociaż stężenie hormonów tarczycy w subklinicznej niedoczynności tarczycy (SNT) mieści się w granicach normy, tak długo jak wydzielanie TSH jest zwiększone, ich stężenie nie odpowiada r zeczywistemu, indywidualnemu zapotrzebowaniu organizmu na hormony. Nieznaczne, chociaż ciągle mieszczące się w zakresie normy przesunięcia w stężeniu fT4 i fT3, mogą mieć znaczenie kliniczne. Do najczęściej stwierdzanych objawów należą: uogólnione zmęczen ie, nietolerancja zimna, suchość skóry, zaparcia, osłabienie siły mięśniowej, chrypka, obrzęki powiek oraz osłabienie procesów pamięciowych. Ryzyko rozwoju klinicznie jawnej niedoczynności tarczycy, jest u tych pacjentów wysokie i wprost proporcjonalne do wysokości TSH. Istnieją dane, że zarówno postać jawna klinicznie, jak i SNT może odpowiadać za wystąpienie u pacjenta dyslipidemii, otyłości i zawartości tkanki tłuszczowej.Mimo że terapia SNT wzbudza duże kontrowersje, większość autorów przychyla się do włączenia terapii L-tyroksyną w przypadku chorych z TSH powyżej 10 mlU/l.There are many causes of hypothyroidism. However, the most common is autoimmune thy - roiditis. Primary hypothyroidism - caused by the thyroid damage, induced by thyroiditis, autoimmune including, thyroidectomy, after treatment with radiation or radioactive iodine, iodine oversupply or insufficiency, drug-induced hypothyroidism, congenital hypothyroidism, enzymatic defects in thyroid hor mone synthesis, or peripheral resistance to thyroid hor mones. Secondary — thyreothropin deficiency (TSH). Tertiary hypothyroidism — thyreolibe - rine deficiency (TRH) caused by tumors of the hypothalamus or h ead trauma with pituitar y stalk interruption. Hypothyroidism, regardless of etiology, can produce a number of diffe - rent symptoms. They may exist in different configurations and d ifferent intensity. Typically, the heavier hypothyroidism is cor related to more symptoms and they are more expressed. Relatively small changes in thyroid hor mone concentration are accompanied by much more pronounced changes in the concentration of TSH. This explains why the increase in TSH reveals faster and at earlier stages of hypothyroidism than changes in fT4 and fT3. However the concentration of thyroid hormones in subclinical hypothyroidism is within normal limits, as long as the secretion of TSH is increased, the concentration does not cor respond to the actual, individual organism needs to hormones . A slight, although still within the normal range changes in the concentration of FT4 and FT3 may have clinical relevance. The most commonly known symptoms include: generalized fatigue, cold intolerance, dry skin, constipation, muscle weakness, hoarseness, swelling of the eyelids and weakness of memory processes. The risk of developing overt hypothyroidism in these patients is high and directly proportional to the amount of TSH. There is evidence that both for m of over t and subclinical hypothyreosis may account for the occur rence of the patient’s dyslipidemia, obesity and body fat exces s. Although the therapy of subclinical hypothyroidism has attracte d considerable controversy, however most authors suppor ts the inclusion of L-thyroxine therapy in patients with TSH greater than 10 mIU/L

Transitions into the negative-energy Dirac continuum

We compare the predictions of the single-particle Dirac equation with quantum field theory for an electron subjected to a space and time dependent field. We demonstrate analytically and numerically that a transition into the negative-energy subspace predicted by the single-particle Dirac equation is directly associated with the degree of suppression of pair-production as described by quantum field theory. We show that the portion of the mathematical wave function that populates the negative-energy states corresponds to the difference between the positron spatial density for systems with and without an electron initially present

Critique of the Wigner tunneling speed and a proposed alternative

In the context of superluminal propagation of wave packets through potential barriers, the tunneling speed is usually characterized by the Wigner velocity. We propose an alternative speed that takes into account the interference between the incoming and the reflected waves and leads to a better estimation of arrival time for a wave packet entering the tunneling region. This arrival time is derived by an extrapolation from inside the barrier. The analytical theory is based on the stationary phase approximation whose validity is justified by a comparison with the numerical solution of the time-dependent Dirac equation

Interpretational difficulties in quantum field theory

Based on space-time-resolved solutions to relativistic quantum field theory we illustrate interpretational difficulties in associating field-theoretical quantities with properties of particles. These difficulties are related to the fact that the definition of the spatial probability density of particles depends on the choice of the Hilbert subspace on which the field operator is projected. We illustrate these problems by analyzing pair-production probabilities and spatial densities for the electron-positron dynamics associated with a spatially localized subcritical potential that is turned on and off in time

Effects of relativity on the time-resolved tunneling of electron wave packets

We solve numerically the time-dependent Dirac equation for a quantum wave packet tunneling through a potential barrier. We analyze the spatial probability distribution of the transmitted wave packet in the context of the possibility of effectively superluminal peak and front velocities of the electron during tunneling. Both the Dirac and Schrodinger theories predict superluminal tunneling speeds. However, in contrast to the Dirac theory the Schrodinger equation allows a possible violation of causality. Based on an analysis of the tunneling process in full temporal and spatial resolution, we introduce an instantaneous tunneling speed that can be computed inside the potential barrier

Electric-field-induced relativistic Larmor-frequency reduction

Using the numerical solution to the time-dependent Dirac equation we show that the effect of relativity on the usual Larmor period for an electron in a magnetic field can be enhanced drastically if a suitably scaled and aligned static electric field is added to the interaction. This electric field does not change the electron\u27s speed but leads to an elliptical spin precession due to relativity. This spin precession is accompanied by a position-dependent spin distribution

Klein paradox with spin-resolved electrons and positrons

Using numerical solutions to relativistic quantum field theory with space-time resolution, we illustrate how an incoming electron wave packet with a definite spin scatters off a supercritical potential step. We show that the production rate is reduced of only those electrons that have the same spin as the incoming electron is reduced. This spin-resolved result further clarifies the importance of the Pauli-exclusion principle for the Klein paradox

Sonographic imaging and differential diagnosis of fetal perineal masses

This case series describes our experience with a prenatal diagnosis of fetal perineal masses. We propose a clinical-sonographic approach for prenatal workup in cases presenting perineal findings based on imaging the target sign at the posterior perineal triangle, the fetal genitalia, and sacrum. Targeted, structured prenatal anatomical scan in fetuses presenting with perineal masses may aid in the prenatal differential diagnosis and enable appropriate genetic analysis, prenatal counseling, and postnatal treatment