Laser-induced level shifts and splittings in multiphoton pair creation

2021 ◽  
Vol 103 (7) ◽  
Author(s):  
D. D. Su ◽  
Y. T. Li ◽  
Q. Su ◽  
R. Grobe
Keyword(s):  
2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
David Vegh

Abstract The classical motion of a Nambu-Goto string in AdS3 spacetime is governed by the generalized sinh-Gordon equation. It can locally be reduced to the sinh-Gordon (shG), cosh-Gordon (chG), or Liouville equation, depending on the value of the scalar curvature of the induced metric. In this paper, I examine solutions that contain both shG-type and chG-type regions. The boundary between these regions moves with the speed of light. I show that near such boundaries (generalized) solitons can be classically pair-produced. The solitons move subluminally (superluminally) in the shG (chG) region on the worldsheet, and they correspond to cusps on the string. A direct energy cascade is observed at the moment of pair-creation.For the calculations, I use an exact discretization of the equation of motion. The solutions are segmented strings. In this discrete system, pair-production leads to a complete evaporation of the shG region. The final state is a gas of cusps in a chG environment.


2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Mohammad H. Al-Qahtani ◽  
Abdullah A. Yousef ◽  
Bassam H. Awary ◽  
Waleed H. Albuali ◽  
Mohammed A. Al Ghamdi ◽  
...  

Abstract Background The Emergency Repartment (ER) is one of the most used areas in healthcare institutions. Problems with over utilisation and overcrowding have been reported worldwide. This study aims at examining the characteristics of paediatric ER visits, the rate of hospital admissions and its associated predictors at King Fahd Hospital of the University in the Eastern Province of Saudi Arabia. Methods This is a retrospective, medical record-based study. Variables included gender, age group, nationality, complaints, Triage level, shifts and seasons. Descriptive statistics were reported as frequencies/percentages. P-values were obtained through a Chi-Squared test while unadjusted and adjusted odds ratios were estimated by binary logistic regression, where admission was considered as the outcome. Results The total number of paediatric patients included was 46,374, and only 2.5% were admitted. Males comprised 55.4% while females comprised 44.6%. The most common age group were toddlers, and 92.4% of the total sample were Saudis. The most common complaint was fever (26.9%) followed by respiratory symptoms (24.9%). Only 7 patients (0.02%) were classified as triage I (Resuscitation), and most were triage IV (Less urgent) (71.0%). Most visits occurred during the winter months. Adjusted ORs showed that neonates had higher odds of admission (OR = 3.85, 95%CI = 2.57–5.76). Moreover, those presenting with haematological conditions showed an OR of 65.49 (95%CI = 47.85–89.64), followed by endocrine conditions showing an OR of 34.89 (95%CI = 23.65–51.47). Triage I had a very high odds of admission (OR = 19.02, 95%CI = 2.70–133.76), whereas triage V was associated with a very low odds of admission (OR = 0.30, 95%CI = 0.23–0.38). Conclusions A low rate of hospital admission was found in comparison with other rates worldwide. This was mostly attributed to an alarmingly high number of non-urgent ER visits. This further emphasises the problem with improper use of ER services, as these cases should be more appropriately directed towards primary healthcare centres. Further studies to examine the impact of prioritising patients in the ER based on the identified predictors of hospital admission, in addition to the standard triage system, are suggested.


2016 ◽  
Vol 31 (02n03) ◽  
pp. 1641031 ◽  
Author(s):  
S. P. Gavrilov ◽  
D. M. Gitman

We consider QED with strong external backgrounds that are concentrated in restricted space areas. The latter backgrounds represent a kind of spatial x-electric potential steps for charged particles. They can create particles from the vacuum, the Klein paradox being closely related to this process. We describe a canonical quantization of the Dirac field with x-electric potential step in terms of adequate in- and out-creation and annihilation operators that allow one to have consistent particle interpretation of the physical system under consideration and develop a nonperturbative (in the external field) technics to calculate scattering, reflection, and electron-positron pair creation. We resume the physical impact of this development.


1998 ◽  
Vol 13 (28) ◽  
pp. 2289-2293 ◽  
Author(s):  
B. C. PAUL ◽  
S. MUKHERJEE ◽  
G. P. SINGH ◽  
A. BEESHAM

The probability for quantum creation of an inflationary universe with a pair of black holes has been studied in semiclassical approximation with Hartle–Hawking boundary conditions, assuming a gravitational action which includes a quadratic term in the scalar curvature αR2, α being a constant. The action of the instanton responsible for creating such a universe, with a spatial section with S1×S2 topology, is seen to be less than that of a de Sitter S3 instanton, unless α<-1/(8Λ), where Λ is the cosmological constant. Since negative α implies a classical instability, the probability for production of primordial black holes seems to be suppressd in R2-theory.


Laser Physics ◽  
2009 ◽  
Vol 19 (8) ◽  
pp. 1735-1742 ◽  
Author(s):  
T. Cheng ◽  
Q. Su ◽  
R. Grobe

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