Comment on ``Reduction of static field equation of Faddeev model to first order PDE'', arXiv:0707.2207

The authors of the article Phys. Lett. B 652 (2007) 384, (arXiv:0707.2207), propose an interesting method to solve the Faddeev model by reducing it to a set of first order PDEs. They first construct a vectorial quantity $\bm \alpha$, depending on the original field and its first derivatives, in terms of which the field equations reduce to a linear first order equation. Then they find vectors $\bm \alpha_1$ and $\bm \alpha_2$ which identically obey this linear first order equation. The last step consists in the identification of the $\bm \alpha_i$ with the original $\bm \alpha$ as a function of the original field. Unfortunately, the derivation of this last step in the paper cited above contains an error which invalidates most of its results

Surgical treatment of Barrett's esophagus with complications

Catedra de Chirurgie Nr 4, Universitatea de Stat de Medicină și Farmacie ,,Nicolae Testemițanu”, IMSP Spitalul Clinic Republican "Timofei Moșneaga", Chișinău, Republica Moldova, Al XIII-lea Congres al Asociației Chirurgilor „Nicolae Anestiadi” și al III-lea Congres al Societății de Endoscopie, Chirurgie miniminvazivă și Ultrasonografie ”V.M.Guțu” din Republica MoldovaIntroducere: Formele asimptomatice de Esofagul Barret (EB) asociat cu displazie determină în timp un risc anual de până la 60% de dezvoltare a adenocarcinomului esofagian, dar și mai frecvent a complicațiilor acute precum ulcere esofagiene, hemoragii digestive superioare (HDS) sau dezvoltarea în timp a stenozelor cicatriceale. Tratamentul complicațiilor determinate de EB reprezintă intervenții chirurgicale laborioase ce au o mortalitate înaltă și o supraviețuire la 5 ani de până la 15%. Material și metode: Un studiu clinic pe serii de cazuri de 62 de bolnavi care au fost diagnosticați și tratați în clinica de chirurgie nr 4 pentru EB pe parcursul a 20 de ani. Complicații ale EB în lotul de cercetare au fost atestate în 22 cazuri (35,4%). Rezultate: Din lotul complicațiilor în 9 cazuri (56%) a fost atestat un adenocarcinom pe fundalul metaplaziei intestinale, 6 cazuri esofag Barrett cu HGD, stenozele au constituit 4 cazuri (40%), iar HDS pe fundalul ulcerului Barrett 3 cazuri (19%). În 100% cazuri acestea au necesitat intervenții chirurgicale rezective, de substituție a esofagului. În 48% din cazuri am utilizat stomacul, în 27% au fost efectuate esofagoplastii cu intestin subtire și în 25% cu colonul. Complicații postoperatorii au fost apreciate în 34% cazuri (dehiscența de anastomoze, fistule), în 5 cazuri (31%) a fost necesară etapizarea intervenției chirurgicale prin aplicarea primară a unei gastrostome, durata medie de spitalizare a constituit 16 zile, iar mortalitate postoperatorie 25%. Concluzii: Complicatile EB deși nu au o incidență înaltă, acestea reprezintă forme evolutive grave cu un prognostic nefavorabil, necesită frecvent intervenții chirurgicale laborioase și au o mortalitate înaltă.Introduction: The asimptomatic forms of BE associated with dysplasia determine a risk up to 60% of evolution into esophageal adenocarcinoma, even more frequent acute complications such as superior digestive hemorrhage or later cicatricial stenosis. The treatment of complications determined by BE represent laborious surgical interventions with a high mortality rate and a 5 year survival rate of 15%. Material and methods: A study comprised of 62 patients, that were diagnosed and treated in Department Nr.4 of Surgery during the last 20 years. Complications of BE in the surveyed batch were determined in 22 cases (35,4%). Results: From the batch with complications, 9 cases (56%) with adenocarcinoma as a result of intestinal metaplasia, 6 cases of Barrett's esophagus with HGD, stenosis - 4 cases (40%), SDH as a consequence of Barrett ulcer – 3 cases (19%). All of them required surgical treatment of esophageal substitution. In 48% stomach was used, in 27 % esophagoplasty with small intestine, 25 % with colon. Postoperative complications occurred in 34 % (anastomotic dehiscence, fistulae), 5 cases (31%) needed split surgery, first being performed the gastrostomy. The average length of hospital stay was 16 days, postoperative mortality – 25%. Conclusions: Even though the complications of BE are rare, they represent severe forms of evolution with an unfavorable outcome that necessitates complicated surgeries with a high mortality rate

Frequency quenching of microwave induced resistance oscillations in a high mobility two-dimensional electron gas

The frequency dependence of microwave-induced resistance oscillations (MIROs) has been studied experimentally in high-mobility electron GaAs/AlGaAs structures to explore the limits at which these oscillations can be observed. It is found that in dc transport experiments at frequencies above 120 GHz, MIROs start to quench, while above 230 GHz, they completely disappear. The results will need to be understood theoretically but are qualitatively discussed within a model in which forced electronic charge oscillations (plasmons) play an intermediate role in the interaction process between the radiation and the single-particle electron excitations between Landau levels.Comment: final version: total 13 pages including 6 figures (6 pages in journal format

Radiation induced oscillations of the Hall resistivity in two-dimensional electron systems

We consider the effect of microwave radiation on the Hall resistivity in two-dimension electron systems. It is shown that the photon-assisted impurity scattering of electrons can result in oscillatory dependences of both dissipative and Hall components of the conductivity and resistivity tensors on the ratio of radiation frequency to cyclotron frequency. The Hall resistivity can include a component induced by microwave radiation which is an even function of the magnetic field. The phase of the dissipative resistivity oscillations and the polarization dependence of their amplitude are compared with those of the Hall resistivity oscillations. The developed model can clarify the results of recent experimental observations of the radiation induced Hall effect.Comment: 4 pages, 1 figur

Absolute Negative Conductivity in Two-Dimensional Electron Systems Associated with Acoustic Scattering Stimulated by Microwave Radiation

We discuss the feasibility of absolute negative conductivity (ANC) in two-dimensional electron systems (2DES) stimulated by microwave radiation in transverse magnetic field. The mechanism of ANC under consideration is associated with the electron scattering on acoustic piezoelectric phonons accompanied by the absorption of microwave photons. It is demonstrated that the dissipative components of the 2DES dc conductivity can be negative ($\sigma_{xx} = \sigma_{yy} < 0$) when the microwave frequency $\Omega$ is somewhat higher than the electron cyclotron frequency $\Omega_c$ or its harmonics. The concept of ANC associated with such a scattering mechanism can be invoked to explain the nature of the occurrence of zero-resistance ``dissipationless'' states observed in recent experiments.Comment: 7 pager, 2 figure

Nonequilibrium phenomena in high Landau levels

Developments in the physics of 2D electron systems during the last decade have revealed a new class of nonequilibrium phenomena in the presence of a moderately strong magnetic field. The hallmark of these phenomena is magnetoresistance oscillations generated by the external forces that drive the electron system out of equilibrium. The rich set of dramatic phenomena of this kind, discovered in high mobility semiconductor nanostructures, includes, in particular, microwave radiation-induced resistance oscillations and zero-resistance states, as well as Hall field-induced resistance oscillations and associated zero-differential resistance states. We review the experimental manifestations of these phenomena and the unified theoretical framework for describing them in terms of a quantum kinetic equation. The survey contains also a thorough discussion of the magnetotransport properties of 2D electrons in the linear response regime, as well as an outlook on future directions, including related nonequilibrium phenomena in other 2D electron systems.Comment: 60 pages, 41 figure

Minimally-invasive surgical treatment of myastenia gravis

IMSP SCR, Secţia Chirurgie Toracică, RM, Chişinău, Al XI-lea Congres al Asociației Chirurgilor „Nicolae Anestiadi” din Republica Moldova și cea de-a XXXIII-a Reuniune a Chirurgilor din Moldova „Iacomi-Răzeșu” 27-30 septembrie 2011Introducere. Miastenia gravis (MG) este o patologie autoimună în care dereglările neuromusculare sunt induse de anticorpii circulanți contra receptorilor acetilcolinici (nAChR) localizați la nivelul postsinaptic al joncțiunii neuromusculare. Abordarea terapeutică a MG presupune un tratament gradual care cuprinde inhibitori de colinesterază pentru simptomatologie minoră şi avansează la medicaţie imunomodulatoare sau plasmafereza pentru situatiile de o gravitate crescută. Timectomia are un rol important în tratamentul complex al MG. Scopul lucrării. Analiza rezultatele postoperatorii ale tratamentului chirurgical videoasistat al miasteniei gravis. Materiale şi metode. În grupul de studiu au fost incluşi 63 pacienți cu MG fără timom observați postoperator mai mult de 12 luni. Repartizarea după sex a fost - 11 bărbați (17,7 %) şi 52 femei (82,5 %), cu vârsta între 18 şi 62 ani. Durata medie a afecțiunii a fost de 21,2 luni, variind mult în cadrul grupului dar fără diferență semnificativă legată de sex. Conform clasificării clinice MGFA pacienți au fost repartizaţi în următoarele stadii : I- 4 (6,3 %) , IIa - 12 (19,04 %), IIb - 17 (26,98 %), III - 13 (20,63 %), IIIb - 12 (19,04 %), IV - 5 (7,94%). Diagnosticul de MG a fost bazat pe examenul clinic neurologic, răspunsul pozitiv la testul cu prozerină sau tensilon, rezultatele tipice electromiografice şi în unele cazuri prin demonstrarea prezenței anticorpilor contra aAChR. Rezultate. Ameliorarea generală a stării pacienților (RCS + AS) a fost demonstrată la 95,23 % pacienți. Ameliorarea stării a fost înregistrată la 42 (66,67 %) pacienți. La 2 pacienți (3,17 %) conform criteriilor noastre (micşorarea scorului QMG ≥ 4 puncte) starea nu s-a modificat după timectomie şi la un pacient (1,59 %) a fost constatată agravarea simptomelor MG în perioada postintervenție. Concluzii. 1. Timectomia toracoscopica este o tehnică avansată de chirurgie miniminvazivă şi este rezervată centrelor cu experienţă atât în chirurgia toracoscopică cât şi în abilitatea de a trata bolnavul miastenic. 2. Factorii de prognostic favorabil depistati în urma analizei multivariate sunt debutul la o vârsta mai tânără a afecţiunii şi intrevenţia chirurgicală precoce faţă de momentul de debut al afecţiunii.Introduction. Myasthenia gravis (MG) is an autoimmune pathology in which neuromuscular disorders are caused by circulating antibodies against acetylcholine receptor (nAChR) located at the postsinaptic level of the neuromuscular junction. Management of MG involves a gradual treatment including cholinesterase inhibitors for minor symptoms and advances to immunomodulating medications or plasmapheresis for high gravity situations. Thymectomy has an important role in the complex treatment of MG. Goal of the study. Analysis of postoperative results of minimally-invasive surgical treatment of myasthenia gravis. Materials and methods. In the study group were included 63 patients with MG without thymoma observed more than 12 months postoperatively. Distribution by sex was - 11 men (17.7%) and 52 women (82.5%), aged between 18 and 62 years. The average duration of disease was 21.2 months, ranging a lot in the group but with no significant differences related to sex. According to clinical classification MGFA patients were divided into the following stages: I-4 (6.3%), IIa - 12 (19.04%), IIb - 17 (26.98%), III - 13 (20.63% ), IIIb - 12 (19.04%), IV - 5 (7.94%). The diagnosis of MG was based on neurological clinical examination, positive response to prozerin or tensilon test, typical electromyographic results and in some cases by demonstrating the presence of antibodies against aAChR. Results. General improvement in the patient’s condition (RCS + AS) has been demonstrated in 95.23% patients. State improvement was recorded in 42 (66.67%) patients. In 2 patients (3.17%) according to our criteria (QMG score decrease ≥ 4 points) status has not changed after thymectomy and in one patient (1.59%) was observed during postoperative period worsening of MG symptoms. Conclusions. 1. Thoracoscopic thymectomy is an advanced technique of minimally-invasive surgery and is reserved to centers with experience in both thoracoscopic surgery and the ability to treat myasthenic patients. 2. Favorable prognostic factors found in multivariate analysis are the onset of disease at a younger age and early surgical treatment from time of onset

Nonlinear effects in microwave photoconductivity of two-dimensional electron systems

We present a model for microwave photoconductivity of two-dimensional electron systems in a magnetic field which describes the effects of strong microwave and steady-state electric fields. Using this model, we derive an analytical formula for the photoconductivity associated with photon- and multi-photon-assisted impurity scattering as a function of the frequency and power of microwave radiation. According to the developed model, the microwave conductivity is an oscillatory function of the frequency of microwave radiation and the cyclotron frequency which turns zero at the cyclotron resonance and its harmonics. It exhibits maxima and minima (with absolute negative conductivity) at the microwave frequencies somewhat different from the resonant frequencies. The calculated power dependence of the amplitude of the microwave photoconductivity oscillations exhibits pronounced sublinear behavior similar to a logarithmic function. The height of the microwave photoconductivity maxima and the depth of its minima are nonmonotonic functions of the electric field. It is pointed to the possibility of a strong widening of the maxima and minima due to a strong sensitivity of their parameters on the electric field and the presence of strong long-range electric-field fluctuations. The obtained dependences are consistent with the results of the experimental observations.Comment: 9 pages, 6 figures Labeling of the curves in Fig.3 correcte