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RISS 인기검색어
- 검색키워드
- 저자 : Bavarsad, Ehsan (검색결과 3 건)
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Schwinger mechanism in electromagnetic field in de Sitter spacetime
Bavarsad, Ehsan,Pyo Kim, Sang,Stahl, Clé,ment,Xue, She-Sheng,Gwak, B.,Kang, G.,Kim, C.,Kim, H.-C.,Lee, C.-H.,Lee, J.,Lee, S.,Lee, W. EDP Sciences 2018 The European Physical Journal Conferences Vol.168 No.-
<P>We investigate Schwinger scalar pair production in a constant electromagnetic field in de Sitter (dS) spacetime. We obtain the pair production rate, which agrees with the Hawking radiation in the limit of zero electric field in dS. The result describes how a cosmic magnetic field affects the pair production rate. In addition, using a numerical method we study the effect of the magnetic field on the induced current. We find that in the strong electromagnetic field the current has a linear response to the electric and magnetic fields, while in the infrared regime, is inversely proportional to the electric field and leads to infrared hyperconductivity.</P>
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Effect of a magnetic field on Schwinger mechanism in de Sitter spacetime
Bavarsad, Ehsan,Kim, Sang Pyo,Stahl, Clé,ment,Xue, She-Sheng American Physical Society 2018 Physical review. D Vol.97 No.2
<P>We investigate the effect of a uniform magnetic field background on scalar QED pair production in a four-dimensional de Sitter spacetime (dS(4)). We obtain a pair production rate which agrees with the known Schwinger result in the limit of Minkowski spacetime and with Hawking radiation in dS spacetime in the zero electric field limit. Our results describe how the cosmic magnetic field affects the pair production rate in cosmological setups. In addition, using the zeta function regularization scheme we calculate the induced current and examine the effect of a magnetic field on the vacuum expectation value of the current operator. We find that, in the case of a strong electromagnetic background the current responds as E . B, while in the infrared regime, it responds as B/E, which leads to a phenomenon of infrared hyperconductivity. These results for the induced current have important applications for the cosmic magnetic field evolution.</P>
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Can STOP Trial Velocity Criteria Be Applied to Iranian Children with Sickle Cell Disease?
Reza Bavarsad Shahripour,Martin M. Mortazavi,Kristian Barlinn,Bijan Keikhaei,Hadi Mousakhani,Mahmoud Reza Azarpazhooh,Morteza Oghbaee,Seyed Aidin Sajedi,Jessica Kepplinger,R. Shane Tubbs,Karen C. Albr 대한뇌졸중학회 2014 Journal of stroke Vol.16 No.2
Background and Purpose: Sickle cell disease (SCD) is strongly linked to stroke across all haplotypes in the pediatric population. Transcranial Doppler (TCD) ultrasound is known to identify the highest risk group in African-Americans who need to receive and stay on blood transfusions, but it is unclear if the same flow velocity cut-offs can be applied to the Iranian population. We aimed to evaluate baseline TCD findings in Iranian children with SCD and no prior strokes. Methods: Children with genetically confirmed SCD (Arabian haplotype, homozygote) and without SCD (controls) were prospectively recruited from pediatric outpatient clinic over a period of 9 months. We performed TCD in both groups to determine flow velocities in the middle cerebral (MCA) and terminal internal carotid arteries (TICA). Results: Of 74 screened children, 60 met the inclusion/exclusion criteria (62% female; mean age 10±4 years). Baseline characteristics did not differ between the cases and controls, except hemoglobin (Hb) which was significantly lower in the SCD group (P<0.001). The right MCA TAMM (Time Averaged Maximum Mean) was significantly higher than in controls (125+ 5.52 cm/s vs. 92.5+1.63 cm/s, P<0.001). Left MCA did not show differences. The TICA TAMM was also different between cases and controls (P<0.05). Conclusions: Among Iranian children with asymptomatic SCD and without receiving recent transfusion TCD velocities are higher as compared to healthy controls but appear much lower than those observed in STOP (Stroke Prevention Trial in Sickle Cell Anemia) studies. We hypothesize that some children at high risk may be present with velocities lower than 170-200 cm/s thresholds. A prospective validation of ethnicity-specific prognostic criteria is warranted.
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