Evolution of Rayleigh-Taylor instability under interface discontinuous acceleration induced by radiation.

Rayleigh-Taylor instability (RTI) under radiation background is commonly found in both engineering applications and natural phenomena. In the optically thin and incompressible limit, the corresponding problem can be simplified as an interface discontinuous acceleration (IDA) RTI problem, but to date has only been studied in the linear stage. In this paper, the entire IDA-RTI evolution was studied numerically and theoretically, particularly for the stages beyond the linear stage. The results show that the IDA-RTI problem is equivalent to the classical RTI with the effective acceleration g_{eff}^{*} that is introduced in this work. Moreover, our studies further show that IDA-RTI can occur if and only if g_{eff}^{*}>0 (from heavy fluid to light fluid). This criterion means that IDA-RTI can occur when (i) heavy fluid supports (or accelerates) the light fluid or (ii) the two fluids have the same density, in contrast to the classical RTI problem. Moreover, the quasisteady bubble and spike velocities are theoretically predicted with quantitative accuracy, showing good agreement with the results of numerical simulations in a wide range of density ratios and acceleration configurations.

Dynamic evolution of Rayleigh-Taylor bubbles from sinusoidal, W-shaped, and random perturbations.

Implicit large eddy simulations of two-dimensional Rayleigh-Taylor instability at different density ratios (i.e., Atwood number A=0.05, 0.5, and 0.9) are conducted to investigate the late-time dynamics of bubbles. To produce a flow field full of bounded, semibounded, and chaotic bubbles, three problems with distinct perturbations are simulated: (I) periodic sinusoidal perturbation, (II) isolated W-shaped perturbation, and (III) random short-wave perturbations. The evolution of height h, velocity v, and diameter D of the (dominant) bubble with time t are formulated and analyzed. In problem I, during the quasisteady stage, the simulations confirm Goncharov's prediction of the terminal speed v_{∞}=Frsqrt[Agλ/(1+A)], where Fr=1/sqrt[3π]. Moreover, the diameter D at this stage is found to be proportional to the initial perturbation wavelength λ as D≈λ. This differed from Daly's simulation result of D=λ(1+A)/2. In problem II, a W-shaped perturbation is designed to produce a bubble environment similar to that of chaotic bubbles in problem III. We obtain a similar terminal speed relationship as above, but Fr is replaced by Fr_{w}≈0.63. In problem III, the simulations show that h grows quadratically with the bubble acceleration constant α≡h/(Agt^{2})≈0.05, and D expands self-similarly with a steady aspect ratio ß≡D/h≈(1+A)/2, which differs from existing theories. Therefore, following the mechanism of self-similar growth, we derive a relationship of ß=4α(1+A)/Fr_{w}^{2} to relate the evolution of chaotic bubbles in problem III to that of semibounded bubbles in problem II. The validity of this relationship highlights the fact that the dynamics of chaotic bubbles in problem III are similar to the semibounded isolated bubbles in problem II, but not to that of bounded periodic bubbles in problem I.

Evolution of mixing width induced by general Rayleigh-Taylor instability.

Turbulent mixing induced by Rayleigh-Taylor (RT) instability occurs ubiquitously in many natural phenomena and engineering applications. As the simplest and primary descriptor of the mixing process, the evolution of mixing width of the mixing zone plays a notable role in the flows. The flows generally involve complex varying acceleration histories and widely varying density ratios, two dominant factors affecting the evolution of mixing width. However, no satisfactory theory for predicting the evolution has yet been established. Here a theory determining the evolution of mixing width in general RT flows is established to reproduce, first, all of the documented experiments conducted for diverse (i.e., constant, impulsive, oscillating, decreasing, increasing, and complex) acceleration histories and all density ratios. The theory is established in terms of the conservation principle, with special consideration given to the asymmetry of the volume-averaged density fields occurring in actual flows. The results reveal the sensitivity or insensitivity of the evolution of a mixing front of a neighboring light or heavy fluid to the degree of asymmetry and thus explain the distinct evolutions in two experiments with the same configurations.

[Clinical features of four atypical pediatric cases of endemic typhus with pneumonia].

OBJECTIVE: To analyze clinical manifestations, treatment and prognosis of 4 cases with endemic typhus. METHOD: The clinical data of four endemic typhus patients in prognosis were retrospectively analyzed. These four atypical cases of endemic typhus with pneumonia were treated in our department from October 2011 to March 2012. They were all male, with an age range of 15 months to 7 years. The four patients had long history, mild respiratory symptom and no improvement was found after treatment with cephalosporins. There were no evidences of bacterial, viral, or fungal infections and we thought they might have infection with other pathogen. Three were from rural areas. Routine blood tests, Weil-Felix reaction, blood smear (Giemsa staining) , and indirect immunofluorescence assay were performed. RESULT: Blood smear and IFA tests showed evidences for endemic typhus. The clinical presentations were atypical, the patients had no headache, but all had fever, rash, and pneumonia of varying severity. None of the patients had a severe cough, but bronchial casts were observed in one case. Recurrent fever was reported in three cases. Physical examinations showed no eschars, but one patient had a subconjunctival hemorrhage, and one had skin scratches, cervical lymphadenopathy, pleural effusion, pericardial effusion, and cardiac dilatation. Two patients had remarkably increased peripheral blood leukocyte counts; both these patients also had high alanine aminotransferase (ALT) levels and one had a high C-reactive protein (CRP) level. Weil-Felix testing was negative or the OX19 titer was low. The peripheral blood smear (Giemsa stain) showed intracellular pathogens in all four cases. After combined therapy with doxycycline and macrolide antibiotics, all four patients recovered well. CONCLUSION: The endemic typhus children often come from rural areas. The clinical presentations were atypical, they usually have no headache, but have fever (often Periodic fever) , rash, and pneumonia of varying severity in these four cases. Combined therapy with doxycycline and macrolide antibiotics was effective in all four patients.

[Clinical analysis of 20 cases with Streptococcus pneumoniae necrotizing pneumonia in China].

OBJECTIVE: Streptococcus pneumoniae necrotizing pneumonia (SPNP) was reported elsewhere but not in China yet. Inappropriate treatment due to poor recognition of this disease could influence its prognosis. This paper presents the clinical characteristics, diagnosis and treatment of SPNP hoping to elevate pediatrician's recognition level for this disease. METHOD: Clinical manifestations, radiological findings, treatment and prognosis of 20 patients (9 boys, 11 girls) who had been hospitalized with SPNP in Beijing Children's Hospital from 2004-2011 were retrospectively analyzed. RESULT: The patients included in this study aged from 9 months to 6 years [(27.9 ± 15.8) m] and were healthy before admission. They were febrile for 8 to 50 days [(27.7 ± 13.5) d] and hospital day was 24 - 55 days [(36.5 ± 8.3) d]. The general condition of all subjects was relatively poor and they all had fever and cough. One child had moderate fever and nineteen children had high fever. Dyspnea was found in sixteen children. Fine rales were found on auscultation in 18 children, among whom diffuse wheeze appeared in 4 children, and wheezy phlegm was found in two children. Signs of pleural effusion were discovered in all cases by physical examination and chest X-ray. White blood cell (WBC) count was 16.2 - 60.95×10(9)/L and neutrophil was 70.5% - 80.2% in peripheral blood routine test. Erythrocyte sedimentation rate (ESR) was 44 - 109 mm/h [(69.6 ± 16) mm/h]and C-reactive protein (CRP) was 80 - > 160 mg/L. The pleural effusion biochemistry and routine test revealed a WBC count of 6400×10(6)/L-too much to count, polykaryocyte of 51% - 90%, glucose of 0.02 - 1.8 mmol/L, protein of 32 - 51 g/L and LDH of 5475 IU/L-or higher. Pleural effusion culture in all cases and blood culture in 2 cases was positive for Streptococcus pneumoniae. Chest X-ray or CT revealed high density and well-distributed lobar consolidation in one lung or two lungs initially. Single or multiple low density lesions in the area of lobar consolidation were found a week later, accompanied by multiple cystic shadow or cavity at the same time or afterwards. Bulla of lung appeared later. Pleural effusions were found in all patients. Seven cases complicated with hydropneumothorax, two with otitis media, one with heart failure, one with cardiac insufficiency. Seventeen patients were treated with vancomycin or teicoplanin or linezolid two with amoxicillin and clavulanate potassium. Other two patients had been treated with meropenem and cephalosporin antibiotics respectively before admission, and they had been at recovery stage when they were hospitalized. Thoracic close drainage and thoracoscopy were performed respectively in 18 cases and 3 cases, respectively. After a follow up of more than 6 months, chest CT showed that almost all lesions in lungs recovered during 4-6 months. No one received pneumonectomy. CONCLUSION: SPNP has special manifestations. The incidence in infants is higher. Patients' general condition is poor and febrile course is relatively long. All patients manifested fever and cough, with a presence of dyspnea in most of them. WBC, neutrophil and CRP elevated apparently. The characteristic of pleural effusion indicates empyema. In early stage, the chest X-ray and CT showed high-density lobar lesions, followed by low-density lesions and cyst gradually. Bulla of lung and/or hydropneumothorax may appear at the late stage. But if diagnosed and treated promptly, the prognosis of SPNP was relatively good.

New species of the isolated Psaroniaceous rachis from the Early Permian in China.

A new kind of marattialean raches are reported from the coal balls in Coal Seam No.7 in the upper part of the Taiyuan Formation (early Early Permian) from Taiyuan, Shanxi, China and are assigned to the genus Stipitopteris Grand'Eury (Psaroniaceae). The present specimens are different from all six reported species of the genus, and are therefore proposed as a new species: Stipitopteris shanxiensis. The raches of the new species are generally dorsi-ventrally flattened. The main raches usually exhibit scales of different forms on their surface. Beneath the epidermis is a zone of parenchymatous cells, some of which contain tannin-like contents. Inside this is a zone of small sclerenchymatous cells. Inward are the ground tissue and vascular bundles. The vascular bundles are continuous and are in two circles: the outer circle assumes a transversely elliptical shape with the gap and pinna trace, and the inner circle assumes a shallow C-shape with inrolled ends. The ground tissue located at the inner side of the vascular bundle is composed of thicker-walled parenchymatous cells. The cells of the ground tissue are vertically elongated in longitudinal sections. Subordered raches are smaller and have simpler structures than the main raches. The parenchyma zone beneath the epidermis is thinner, usually one to two cells wide and the sclerenchyma zone is usually absent. The scales are poorly developed and there is only one C-shaped vascular bundle. The new species is comparable to the crosiers of Psaroniaceae of the Euramerican Flora in some aspects, for example, it has a dorsi-ventrally flattened rachis and scales on the surface of the rachis. However, the other features and the preservative conditions of the present specimens indicate that they are not crosiers, but fully developed or mature raches. The new species is the first well-studied anatomically-preserved rachis of Psaroniaceae from the Cathaysian Flora and bears significance not only in understanding the anatomy and taxonomy of Psaroniaceae in the Cathaysian Flora, but also in the relationship between the Euramerican Flora and the Cathaysian Flora.

Protective effect of sericin peptide against alcohol-induced gastric injury in mice / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Sericin peptide (SP) has shown a powerful anti-oxidant property in a host of studies. The present study was designed to investigate the possible protective effects of SP against alcohol-induced gastric lesions in mice and to explore the potential mechanisms.</p><p><b>METHODS</b>Animals were randomly divided into 5 groups: control, alcohol (56%, 14.2 ml/kg), SP-treated mice (0.2, 0.4, 0.8 g/kg). Mice were pretreated with SP before administering alcohol, the concentration of ethanol in serum and urine, the contents of malondialdehyde (MDA), glutathione (GSH) and the glutathione peroxidase (GSH-PX), catalase (CAT) and superoxide dismutase (SOD) activities in the gastric mucosa were measured, subsequently, the pathological evaluation of stomach was also observed.</p><p><b>RESULTS</b>Of the animals pre-treated with SP (0.4, 0.8 g/kg), the concentration of ethanol in serum was significantly decreased, while increased in urine as compared to the alcohol-administered alone animals. Alcohol administration caused severe gastric damage as indicated by markedly increased MDA levels and decreased antioxidants, such as reduced GSH, GSH-PX and SOD in the gastric tissue while the CAT activity was not altered. On SP administration there was a reversal in these values towards normal. Histopathological studies confirmed the beneficial role of SP, which was in accordance with the biochemical parameters.</p><p><b>CONCLUSIONS</b>SP could protect gastric mucosa from alcohol-induced mucosal injury. These gastroprotective effects might be due to increasing 'first-pass metabolism' in the stomach and hastening ethanol elimination directly through the urine. SP might also play an important role in the protection of the structure and function of gastric mitochondria, at least partly based on their anti-oxidant effect.</p>