Stabilization and Ionization Suppression in Intense Pulsed Fields.

The phenomenon of stabilization and ionization suppression in intense pulsed fields is investigated for systems initially in their ground states. This is done by considering one-dimensional model potentials which include one bound state and many bound states. The phenomenon of intense field stabilization is found to exist for both types of potentials while the pulse is on. However, it is discovered that this is not accompanied by suppression of ionization at the end of the pulse in all regimes of the peak field strength. The main features of the variation of the ionization probability with the peak field strength are: an initial decrease followed by an upturn and finally a tendency toward saturation. The upturn is found to be predominantly due to the non-adiabatic evolution of the system during the turn-on stage of the pulse. The saturation of the ionization probability at very high field strengths is traced to the near similarity of the wave functions prior to the beginning of the turn-off for several different peak field strengths in the saturation regime. This in turn results from the reduced interaction between the potential and the wave function during the pulse

Meningiomas: Correlation of Ki67 with histological grade

Background : Meningiomas are slow-growing tumors. Grading of meningiomas based on histological features has certain limitations in predicting the exact biological behavior, necessitating ancillary techniques. Objective : To study the Ki67 labeling index (Ki67 LI) in various histological subtypes and grades of meningioma and correlate it with various parameters for recurrence. Material and Methods : All intracranial and intraspinal meningiomas diagnosed between 2005 and 2008 were graded according to WHO 2007 criteria. Immunohistochemistry was performed using Ki67 (Dako, USA 1:50) in 300 cases. Statistical analysis was performed. Results : There was female predominance. The age ranged from 2-75 years including 11 children below the age of 18 years. There were 211 Grade I, 78 Grade II and 11 Grade III meningiomas. The mean Ki67 LI increased from Grade I to II and from Grade II to III and these were statistically significant. The Ki67 LI was high for the subtypes of clear cell, chordoid, papillary and rhabdoid but there was no statistical significance between the subtypes. The difference in Ki67 LI between recurrent versus non-recurrent and brain-invasive versus non-invasive meningiomas was statistically significant. Conclusion : High Ki67 LI indicates higher grade of meningioma. The difference in KI67 LI between recurrent and non-recurrent meningiomas was statistically significant

Teratomas in central nervous system: A clinico-morphological study with review of literature

Background: Cranio-spinal axis teratomas are rare. This subset is interesting because symptoms can be varied, depending on the location. Histopathology is diagnostic; most of the lesions are benign. Rarely, malignancy develops in any of the somatic components. Aims: To study the demographic, clinico-morphological and follow-up data of central nervous system (CNS) teratomas. Materials and Methods: Cases diagnosed as mature or immature teratomas in the CNS over a 20-year period were included in the study. Clinico-radiological, demographic and follow-up data of these cases were analyzed. Results: A total of 14 tumors were diagnosed as teratomas. Of these, 11 were mature cystic teratomas; and 1 case each, of teratoma with malignant transformation, terato-carcinoma and mixed germ cell tumor (immature teratoma with germinoma). Six of the 14 cases were intracranial and 8 were spinal. Presenting features varied according to the location. Radiologically, contrast enhancement with predominantly solid component was suggestive of malignancy or an aggressive tumor. Morphologically, a variety of tissue derivatives were seen in the cases. Excision was curative or provided symptomatic relief in most cases; terato-carcinoma and mixed germ cell tumor patients needed adjuvant radiotherapy. Conclusion: CNS teratomas are rare. Morphology and location decide outcome

Passivation of Germanium by Graphene

The oxidation of Ge covered with graphene that is either grown on or transferred to the surface is investigated by X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy. Graphene properly grown by chemical vapor deposition on Ge(100), (111), or (110) effectively inhibits room-temperature oxidation of the surface. When graphene is transferred to the Ge surface, oxidation is reduced relative to that on uncovered Ge but has the same power law dependence. We conclude that access to the graphene/Ge interface must occur via defects in the graphene. The excellent passivation provided by graphene grown on Ge should enhance applications of Ge in the electronic-device industr