Evidence for a Quantum Hall Insulator in an InGaAs/InP Heterostructure

We study the quantum critical behavior of the plateau-insulator (PI) transition in a low mobility InGaAs/InP heterostructure. By reversing the direction of the magnetic field (B) we find an averaged Hall resistance \rho_xy which remains quantized at the plateau value h/e^2 throughout the PI transition. We extract a critical exponent \kappa'= 0.57 +/- 0.02 for the PI transition which is slightly different from (and possibly more accurate than) the established value 0.42 +/- 0.04 as previously obtained from the plateau-plateau (PP) transitions.Comment: 3pages, 2 figures; submitted to EP2DS-14 conference proceeding

Critical behavior of thermopower and conductivity at the metal-insulator transition in high-mobility Si-MOSFET's

This letter reports thermopower and conductivity measurements through the metal-insulator transition for 2-dimensional electron gases in high mobility Si-MOSFET's. At low temperatures both thermopower and conductivity show critical behavior as a function of electron density which is very similar to that expected for an Anderson transition. In particular, when approaching the critical density from the metallic side the diffusion thermopower appears to diverge and the conductivity vanishes. On the insulating side the thermopower shows an upturn with decreasing temperature.Comment: 4 pages with 3 figure

Primary extra-cranial meningioma of head and neck : clinical, histopathological and immunohistochemical study of three cases

I meningiomi extracranici della regione testa-collo sono neoplasie rare, dal momento che la maggior parte di esse risulta essere una localizzazione secondaria di un tumore primitivo intracranico. Vengono di seguito descritti tre casi clinici di meningioma extracranico localizzati nel muscolo temporale, nella ghiandola parotide e nella cavit\ue0 nasale. L\u2019asportazione chirurgica \ue8 il trattamento di elezione e la prognosi di questo tipo di neoplasia \ue8 generalmente eccellente. Per la diagnosi differenziale istopatologica di queste neoplasie \ue8 necessario considerare i tumori pi\uf9 comuni della regione testa-collo. In particolare l\u2019esame istopatologico perioperatorio \ue8 molto utile nell\u2019indirizzare il trattamento chirurgico e dovrebbe essere sempre eseguito per escludere la natura maligna della lesione evitando un \u201cover-treatment\u201d. I nostri pazienti sono stati sottoposti ad intervento chirurgico e sono attualmente in buono stato di salute dopo il trattamento.Extracranial meningiomas of the head and neck region are rare neoplasms, the majority being a secondary location of a primary intracranial tumour. We herewith report three rare cases of extracranial meningiomas, located in the temporal muscle, parotid gland and nasal cavity, together with complete pathological, immunohistochemical and ultrastructural studies. Prognosis of this tumour is generally excellent. Surgical excision is the treatment of choice, with no need for further treatment; nevertheless, differential diagnosis must consider other more common tumours of the head and neck and be based on histopathologic examination and relative techniques, including examination of frozen sections. This procedure is particularly useful assessing surgical treatment and should be performed whenever possible to exclude the malignant nature of the lesion and avoid over-treatment. All three patients underwent surgery and are alive and disease-free

Polycyclic Aromatic Hydrocarbons in Air

Policiklički aromatski ugljikovodici (PAU) spojevi su koji se sastoje od dva ili više kondenziranih aromatskih prstenova. Nastaju prilikom nepotpunog izgaranja ili pirolize organskih tvari. Dokazano je da neki PAU imaju kancerogena, a neki mutagena svojstva, pa je stoga potrebno kontinuirano pratiti koncentracije PAU u zraku, vodi i tlu, te pokušati sanirati izvore PAU. PAU s dva ili tri aromatska prstena postojani su u plinovitoj fazi, dok se PAU s više aromatskih prstenova nalaze u zraku uglavnom vezani na čestice. Visoke koncentracije PAU prisutne su u atmosferi urbanih područja, a najviše su zimi kada su pojačane emisije iz kućnih ložišta. U ljetno doba koncentracije su niže jer je većina policikličkih aromatskih ugljikovodika nestabilna na visokim temperaturama, a osim toga dolazi do njihove oksidacije i fotooksidacije. Metode mjerenja PAU u zraku uključuju uzorkovanje prosisavanjem na filterski papir ili kruti adsorbens, ekstrakciju i kromatografsku analizu. U ovom radu prikazani su rezultati mjerenja benzo[a]pirena (BaP) kao glavnog predstavnika PAU na nekim lokacijama u svijetu. Razine BaP u svijetu uspoređene su s rezultatima mjerenja provedenim do sada u Hrvatskoj.Polycyclic aromatic hydrocarbons (PAHs) are a large group of organic compounds consisting of two or more condense aromatic rings. They are products of incomplete combustion or pyrolysis of organic matter. Because some PAHs such as Benzo[a]pyrene (BaP) are proven carcinogens and mutagens, it is necessary to continuously monitor their concentrations in the air, water, and soil. PAHs with two or three aromatic rings are stable in the gas phase, while most PAHs with five or more aromatic rings bond to particles. Higher concentrations of PAHs are present in the atmosphere of urban areas, mostly in the winter, due to heating. In the summer, these concentrations drop because most PAHs are unstable at high temperatures and break down by oxidation and photooxidation. Measurements of PAHs in the air include sampling on the filter paper or solid adsorbent, extraction, and chromatographic analysis. This review presents the measurements of BaP in some locations in the world and compares them with the findings in Croatia

Conductance and diffusion of a SiGe two-dimensional hole gas in magnetic field

Contains fulltext : 60695.pdf (publisher's version ) (Open Access)RU Radboud Universiteit Nijmegen, 28 juni 2004Promotor : Maan, J.C.109 p

Thermopower of a p-type Si/Si1-xGex heterostructure

Contains fulltext : 60252.pdf (author's version ) (Open Access)We report thermopower measurements in zero and low magnetic fields for a p-type Si/Si1-xGex heterostructure. The diffusion components of both the longitudinal and transverse components are reasonably well described by the Mott approach, including the quantum oscillations at low magnetic fields. The magnetic-field dependence of thermopower shows that the diffusion contribution at zero field deviates from the linear temperature dependence that would be expected for a degenerate system, probably as a result of the nearby metal-insulator transition. Phonon drag also does not behave as expected. Instead of exhibiting an approximate T-6 dependence at low temperatures appropriate to screened, hole-phonon, deformation-potential scattering, an approximate T-4 dependence is observed. This is consistent with previous observations on the energy-loss rates in SiGe hole systems. The experimental data on drag are in good agreement with numerical calculations by assuming either hole-phonon scattering by an unscreened deformation-potential interaction or by assuming a screened piezoelectric plus screened deformation-potential coupling