Effect of Thermal and Structural Disorder on the Electronic Structure of Hybrid Perovskite Semiconductor CH3NH3PbI3.

In this Letter, we investigate the temperature dependence of the optical properties of methylammonium lead iodide (MAPbI3 = CH3NH3PbI3) from room temperature to 6 K. In both the tetragonal (T > 163 K) and the orthorhombic (T < 163 K) phases of MAPbI3, the band gap (from both absorption and photoluminescence (PL) measurements) decreases with decrease in temperature, in contrast to what is normally seen for many inorganic semiconductors, such as Si, GaAs, GaN, etc. We show that in the perovskites reported here, the temperature coefficient of thermal expansion is large and accounts for the positive temperature coefficient of the band gap. A detailed analysis of the exciton line width allows us to distinguish between static and dynamic disorder. The low-energy tail of the exciton absorption is reminiscent of Urbach absorption. The Urbach energy is a measure of the disorder, which is modeled using thermal and static disorder for both the phases separately. The static disorder component, manifested in the exciton line width at low temperature, is small. Above 60 K, thermal disorder increases the line width. Both these features are a measure of the high crystal quality and low disorder of the perovskite films even though they are produced from solution.

Band Gap Tuning of CH3NH3Pb(Br(1-x)Clx)3 Hybrid Perovskite for Blue Electroluminescence.

We report on the structural, morphological and optical properties of AB(Br(1-x)Cl(x))3 (where, A = CH3NH3(+), B = Pb(2+) and x = 0 to 1) perovskite semiconductor and their successful demonstration in green and blue emissive perovskite light emitting diodes at room temperature. The bandgap of perovskite thin film is tuned from 2.42 to 3.16 eV. The onset of optical absorption is dominated by excitonic effects. The coulomb field of the exciton influences the absorption at the band edge. Hence, it is necessary to explicitly account for the enhancement of the absorption through the Sommerfield factor. This enables us to correctly extract the exciton binding energy and the electronic bandgap. We also show that the lattice constant varies linearly with the fractional chlorine content satisfying Vegards law.

Separating Charges at Organic Interfaces: Effects of Disorder, Hot States, and Electric Field.

Charge separation at organic-organic (O-O) interfaces is crucial to how many organic-based optoelectronic devices function. However, the mechanism of formation of spatially separated charge carriers and the role of geminate recombination remain topics of discussion and research. We review critically the contributions of the various factors, including electric fields, long-range order, and excess energy (beyond the minimum needed for photoexcitation), to the probability that photogenerated charge carriers will be separated. Understanding the processes occurring at the O/O interface and their relative importance for effective charge separation is crucial to design efficient solar cells and photodetectors. We stress that electron and hole delocalization after photoinduced charge transfer at the interface is important for efficient free carrier generation. Fewer defects at the interface and long-range order in the materials also improve overall current efficiency in solar cells. In efficient organic cells, external electric fields play only a small role for charge separation.

Role of preoperative 3D CT reconstruction for evaluation of patients with esophageal atresia and tracheoesophageal fistula.

OBJECTIVE: The role of preoperative contrast-enhanced computerized tomography (CT) of chest with three-dimensional (3D) reconstructions was evaluated in neonates with esophageal atresia and tracheoesophageal fistula. METHODS: This was a prospective study which investigated 30 cases of esophageal atresia with tracheoesophageal fistula. All patients were evaluated preoperatively with contrast-enhanced spiral CT using a low-dose CT protocol. 3D CT reconstruction images were evaluated for the type of esophageal atresia, the distance between the upper and lower esophageal pouches, origin, level and position of the fistula, and the presence or absence of any other cardiac, pulmonary or mediastinal lesions and the findings were correlated with the findings at surgery. The radiation dose for each patient was calculated using the formula-Effective dose (E) = DLP × (E/DLP)age. RESULTS: All the 30 cases had type-C esophageal atresia with tracheoesophageal fistula as per Gross classification. The exact site of the fistula could be identified only in 26 (80 %) cases. The mean gap between the upper pouch and lower fistula was 0.95 ± 0.57 cm (range 0.2-2.8 cm) on CT scan and 1.38 ± 0.61 cm (range 0.5-3.2 cm) at surgery. On statistical analysis, the correlation was found to be significant (p < 0.0001). In addition, lung pathology (consolidation), cardiac pathology and vertebral anomaly were also detected on CT scan in some cases. The mean radiation dose for the neonates who underwent CT chest was calculated to be 1.79 mSv which is significantly high. CONCLUSION: Though preoperative CT scan of chest has many advantages, it involves significant exposure to ionizing radiation and risk of radiation-induced cancer in the future. Additionally in 20 % of cases, the fistula could not be located on CT scan. The most common variety of esophageal atresia and tracheoesophageal fistula is Gross type C (86 %) that has low to intermediate gap (97 %) and can be anastomosed primarily. Thus, CT scan can provide good anatomical delineation, but may not help in surgical decision making. Hence, performing CT in these cases would unnecessarily expose the neonates to ionizing radiation. Therefore, there is no role for CT scan in the routine preoperative assessment of EA with distal TEF.

Mini-vesicostomy in the management of PUV after valve ablation.

AIM: To determine the usefulness of infra-umbilical mini-vesicostomy in infants with posterior urethral valves (PUV), in developing countries. This new technique facilitates clean intermittent catheterization (CIC) and overnight bladder drainage, which have been effectively used for the treatment of valve bladders in the developed world. METHODS: A retrospective analysis of the records of three infants who underwent a mini-vesicostomy between 2005-2009 was done. All were put on CIC in the neonatal period. Monitoring of renal parameters, bladder function and structural changes in the bladder was done before and after 4 years of CIC. RESULTS: All three showed a decrease in upper tract dilatation, improvement in cortical function and improvement of bladder compliance at the end of 4 years. Two patients are on CIC through vesicostomy and can pass a good stream of urine per urethraly, and in one the vesicostomy has been closed. CONCLUSION: Mini-vesicostomy is a useful option to allow CIC on a long-term basis in children with PUV. There were no complications with this technique in this small group of patients, and it has been well accepted by their families.

Multiple indomethacin-induced colonic perforations in an adolescent.

Colonic perforation is an uncommon cause of acute abdomen in paediatric patients, and can present a diagnostic enigma as well as management challenge to the paediatric surgeon. An adolescent developed multiple colonic perforations following a short course of oral indomethacin, requiring emergency hemicolectomy. This is the youngest known case of enteral non-steroidal anti-inflammatory drug (NSAID)-mediated large bowel injury. We review current evidence on NSAID-related enteropathy, and postulate potentiating mechanisms that may have accounted for the unusually rapid clinical course of our patient.

Transanal Swenson's operation for recto-sigmoid Hirschsprung's disease.

BACKGROUND: Transanal Swenson's operation is a relatively new single-stage procedure for Hirschsprung's disease. The results of this procedure at our centre are presented. PATIENTS AND METHODS: Seventeen patients of recto-sigmoid Hirschsprung's disease underwent single-stage transanal Swenson's procedure. The diagnosis was based on the evidence of a transition zone on barium enema examination. A full thickness incision was made on the rectal wall posteriorly, 0.5 cm above the dentate line. The mobilised segment was resected about 5 cm above the transition zone. Frozen sections were performed whenever the transition zone was not clearly seen intra-operatively. The operation was completed by full thickness colo-anal anastomosis. RESULTS: There were fourteen male and three female patients. The ages of the patients ranged from two months to eight years (median 14 months). The median hospital stay was four days (range four to seven days). Two patients required additional abdominal mobilisation. The anatomical transition zone as seen intra-operatively correlated with the pathological transition zone in all the cases. Two patients had episodes of post-operative enterocolitis and the other two patients developed stricture of the anastomosis. The follow-up period ranged from six to 45 months (Mean 35.4 months). Post-operative soiling was observed in all the patients and lasted from two to six weeks (Mean 3.4 weeks). There were no injuries to the surrounding structures. No patient had voiding disturbances and post-void residual urine was normal in all the patients. Initial increased frequency of bowel movements had settled to one to three per day. CONCLUSIONS: Transanal Swenson's pull through not only avoids laparotomy, but also the problems associated with the muscular cuff of transanal endorectal pull-through. The anatomical transition zone can be safely utilised to decide the resection limits. By a meticulous technique of dissection, injury to the surrounding structures can also be avoided.

Management of duodenal perforation following upper gastrointestinal endoscopy. A safe and feasible alternative.

Upper gastrointestinal endoscopy has been increasingly used in children for various diagnostic and therapeutic purposes. But this has not always been a morbidity free procedure especially in small kids. Three patients who presented with history of endoscopic intervention followed by abdominal pain and radiographic evidence of free air under diaphragm were managed conservatively over a period of two years.

Role of shunts with antisiphon device in treatment of pediatric hydrocephalus.

OBJECTIVE: The use of ventriculo-peritoneal shunts having antisiphon device has been reported in adult patients, but there is a dearth of experience with such shunts in pediatric age group. This study is being undertaken to compare the effectiveness of these types of shunt for the treatment of congenital hydrocephalus. PATIENTS AND METHODS: Forty patients with congenital hydrocephalus with or without neural tube were divided randomly into two groups (A and B). Patients in antisiphon group were treated with shunts with differential valve including antisiphon device (Vygon shunt) while patients in non-antisiphon group were treated with differential valve shunts (Chhabra shunt and Ceredrain). Mann-Whitney test, asymmetric t-test and Chi-square test were used to assess the correlation and the significance. RESULTS: The mean age was 3.5 months and 3.4 months in antisiphon group and non-antisiphon group, respectively. The M:F ratio was 2.3:1 in antisiphon group while it was 3:1 in non-antisiphon group. The mean decrease in OFC was more in non-antisiphon group than antisiphon group during the follow up from 3 months to 6 months while mean decrease in MEI was more in non-antisiphon group from 0 month to 3 months than antisiphon group. There were two cases of shunt overdrainage in non-antisiphon group. The shunt blockage rate was 20% in antisiphon group and 15% in non-antisiphon group, respectively. There was 20% and 15% shunt infection rate in antisiphon group and non-antisiphon group, respectively. This study demonstrated overdrainage syndrome in two of the patients of differential valve shunts. CONCLUSION: Though rare, complication associated with overdrainage is certainly a problem in children. In our study, the patients who received shunts with antisiphon device do not show any overdrainage.

Prophylactic embolization of hepatic artery pseudoaneurysm after blunt abdominal trauma in a child.

We describe a 10-year-old boy who developed a pseudoaneurysm in the territory of the left hepatic artery after blunt trauma to the abdomen, which was prophylactically embolized. He was discharged early and was able to return to activities of daily life. In view of the potentially fatal complication of severe hemorrhage from a missed hepatic pseudoaneurysm rupture, recognition and early embolization of a traumatic pseudoaneurysm of hepatic artery are recommended. This decreases morbidity, mortality, and length of hospital stay and allows for early mobilization especially in children who are difficult to restrain in bed.

Role of tracheostomy in the management of foreign body airway obstruction in children.

INTRODUCTION: Foreign body aspiration in the airway of children is a life-threatening clinical situation. Endoscopic retrieval alone is successful in the majority of patients. Occasionally, open surgical intervention in the form of tracheostomy, thoracotomy and bronchotomy and/or pulmonary resection is needed. We analysed the specific indications for tracheostomy during the removal of airway foreign bodies in our study. METHODS: The records of four patients who needed tracheostomy, out of 342 cases of foreign body airway obstruction managed by the senior author, were analysed. These patients underwent an additional tracheostomy for open removal of the foreign body and/or to secure the airway to facilitate the foreign body removal. RESULTS: Rigid bronchoscopy was successful in retrieving the foreign bodies in 338 (98.8 percent) cases, while four (1.2 percent) cases required additional tracheostomy, either to protect the airway during the procedure or to assist in removing the foreign body. The indications for tracheostomy were subglottic foreign bodies of long duration, sharp subglottic foreign bodies and foreign bodies that were larger than the glottic chink. There was no mortality or long-term complication because of the tracheostomies. CONCLUSION: Tracheostomy is occasionally indicated in foreign body extraction, when they are subglottic in location and impacted, or are large foreign bodies that get obstructed at the glottic chink during removal.

Multicystic dysplastic kidney in children--a need for conservative and long term approach.

OBJECTIVE: We retrospectively studied our cases of Multicystic Dysplastic Kidney (MCDK). The review was aimed at identifying the pattern of the disease in Indian Scenario and the required management thereof. METHODS: We studied the clinical, radiological and nuclear scan findings of 22 patients with unilateral MCDK. They were diagnosed and/or treated in our unit from 1999 to 2007. The diagnosis was achieved by Ultrasound and further confirmed by DMSA scans. Other ancillary investigations like Micturating cystourethrogram were done if indicated. These patients were followed and followup investigations consisted of renal ultrasound, blood pressure measurement, and urinalysis and blood biochemistry RESULTS: A total of 22 patients (18 boys and 4 girls) with unilateral MCDK were investigated and followed for a mean period of 41 months. MCDK was detected on antenatal ultrasound only in 12(55%) and postnatally in 10(45%) babies. Mean age for postnatal diagnosis was 20 months. Follow up ultrasound revealed complete involution of MCDK in 3 patients and partial regression in 11 patients. The size of dysplastic kidney was unchanged in 4 patients and a further 4 patients underwent nephrectomy. Indications of nephrectomy were parental anxiety in 2, hypertension in 1 and palpable mass in 1. CONCLUSION: Large proportion (45%) of patients in presented series are diagnosed post natally contrary to western world where more than 80% are diagnosed antenatally. Uncomplicated isolated MCDK carry good prognosis with nephrectomy required in only a few patients. Association with other urological anomalies in ipsilateral/contralateral genitourinary tract is important to identify as they have worse outcome in terms of ultimate renal function. All patients with simple/complex unilateral MCDK should be advised long term follow up for the possible development of hypertension and/or hyper infiltration injury.

2, 8 Dihydroxyadenine urolithiasis: A case report and review of literature.

Adenine phosphoribosyl transferase deficiency is a rare metabolic abnormality presenting with 2,8 dihydroxyadenine urolithiasis. The stones are characteristically radiolucent and therefore need to be differentiated from uric acid stones which are also radiolucent and have identical chemical reactivity. No cases of 2, 8- dihydroxyadenine urolithiasis have been reported from India. We report a 3 year old child with 2, 8- dihydroxyadenine urolithiasis and acute renal failure.

Risk factors for renal injury in patients with meningomyelocele.

PATIENTS AND METHODS: Thirty operated patients of myelodysplasia were clinically evaluated for the age at presentation, the extent of lesion and neurological deficit. Urological assessment was done with urine cultures, serum creatinine, radiological (ultrasound of kidney, ureters and bladder, voiding cystourethrogram) and urodynamic (water cystometry) parameters. An objective scoring for bladder (Galloway, et al.) was applied. Dimercapto-succinic acid (DMSA) scan was done in all the patients for evidence of renal scars. The results of above investigations were correlated with presence or absence of renal scars (renal injury) on DMSA scan. None of the patients had received any prior bladder care. RESULTS: Twenty one patients had no renal scars and 9 patients had evidence of renal scarring. Patients with renal scars were older at presentation, they had greater degree of hydroureteronephrosis (P < or = 0.001) and vesicoureteric reflux (P < or = 0.005). The incidence of high leak pressures (>25 cm of water, P < or = 0.05), unacceptable bladder volumes (maximum cystometric capacity < 60% for age, P < or = 0.005) and high risk Galloway's score (> 5, P < or = 0.05) was high in patients with associated renal scarring as compared to their nonscarred counterparts. Three of these patients had serum creatinine >1 mg/dl (P < or = 0.005). The incidence of urinary complaints and positive urine cultures was also higher in these patients (NS). CONCLUSION: Increasing age, evidence of hydroureteronephrosis and vesicoureteric reflux, high leak pressures, low bladder volume and high combined Galloway score (>5) define a high risk bladder in our population and predispose to renal injury in patients of myelodysplasia. Early referral for bladder risk assessment and management of all myelodysplasia patients is recommended.

Postauricular congenital alveolar rhabdomyosarcoma- a case report of an unusual entity.

BACKGROUND: Congenital alveolar rhabdomyosarcoma is an extremely uncommon and invariably fatal tumor with the current therapy. Less than 25% of patients present with evidence of cutaneous metastasis. CASE PRESENTATION: We report a case of congenital alveolar rhabdomyosarcoma in an 18-month-old male who presented with a progressively increasing mass lesion in the left post-auricular region since birth. Radiological examination did not show any intracranial involvement of the mass lesion. Upon resecting the mass that was 10-cm in largest dimension, the gross, microscopic, and ultrastructural findings were consistent with congenital alveolar rhabdomyosarcoma. CONCLUSION: The suspicion of alveolar subtype on histological grounds and proper evaluation of this tumor by immunostain and ultrastuctural examination is necessary. In the Medline literature search, there is no report of large congenital alveolar rhabdomyosarcoma in the post-auricle region.

Factors affecting renal scarring in posterior urethral valves.

AIM: To retrospectively review the occurrence of renal scarring in patients with posterior urethral valves (PUV), and correlate it with various causative factors. METHODS: The records of 52 patients treated for PUV by the authors were reviewed. Patients with vesico-ureteric reflex (VUR) dysplasia syndrome were excluded from the study. The patients were divided into group I (no renal scarring, n=18) and group II (renal scars present, n=34) based on dimercapto-succinic acid scans. The mode of treatment, presence/absence of breakthrough urinary tract infections (UTI), presence/absence of history of nocturnal/diurnal incontinence, presence/absence of VUR, stable postoperative serum creatinine, rate of drainage of ureters on diethylene triamine penta acetic acid (DTPA) scans and management of bladder dysfunction, if any, were noted. The presence or absence of renal scarring was statistically correlated with occurrence of any of the above factors. RESULTS: Primary valve fulguration was performed in 41 patients and 11 patients had an initial vesicostomy. The median follow up was 3.5 years (range 1.5-15 years). Renal scarring was present in either kidney in 34 patients (bilateral 14, unilateral 20). The mode of initial treatment did not affect the incidence or rate of scarring. The preoperative and postoperative serum creatinine at the end of 1 year did not differ between the two groups. Presence/severity of VUR did not affect the pattern of renal scarring. A highly significant correlation between the occurrence of renal scarring and presence of diurnal incontinence (P< or =0.007, odds ratio=4.5) and breakthrough UTI (P< or =0.002, odds ratio=7.0) was observed. There was also correlation with slow drainage in the ureters on a DTPA scan (P< or =0.0005). Detrusor instability and low compliance on urodynamic assessment did not affect occurrence in the limited number of patients studied. The rate of somatic growth in both groups was retarded as compared to normal healthy counterparts. CONCLUSION: Breakthrough UTI, diurnal incontinence and poor drainage of ureters on DTPA are associated with a higher incidence of renal scarring. Mode of initial treatment, presence or absence of VUR, and bladder abnormalities do not affect renal scarring in the short term.