Femtosecond Population Inversion and Stimulated Emission of Dense Dirac Fermions in Graphene

We show that strongly photoexcited graphene monolayers with 35fs pulses quasi-instantaneously build up a broadband, inverted Dirac fermion population. Optical gain emerges and directly manifests itself via a negative optical conductivity for the first 200fs, where stimulated emission completely compensates absorption loss in the graphene layer. Our experiment-theory comparison with two distinct electron and hole chemical potentials reproduce absorption saturation and gain at 40fs, revealing, particularly, the evolution of the transient state from a hot classical gas to a dense quantum fluid with increasing the photoexcitation

Femtosecond Population Inversion and Stimulated Emission of Dense Dirac Fermions in Graphene

We show that strongly photoexcited graphene monolayers with 35 fs pulses quasi-instantaneously build up a broadband, inverted Dirac fermion population. Optical gain emerges and directly manifests itself via a negative conductivity at the near-infrared region for the first 200 fs, where stimulated emission completely compensates absorption loss in the graphene layer. Our experiment-theory comparison with two distinct electron and hole chemical potentials reproduce absorption saturation and gain at 40 fs, revealing, particularly, the evolution of the transient state from a hot classical gas to a dense quantum fluid with increasing the photoexcitation

Stochastic coarsening model for Pb islands on a Si(111) surface

The coarsening behavior of individual Pb islands on Si(111) surface has been studied by scanning tunneling microscopy. Traditionally island decay follows a smooth power-law dependence on the time until disappearance. In Pb/Si(111), some unstable islands are inactive for a long time but once their decay is triggered they suffer a “sudden death.” Four-layer islands are found to decay rapidly, increasing the area covered by seven-layer islands. All islands, decaying or otherwise, are accompanied by island size fluctuation which involve a large number of perimeter atoms moving collectively as a “quantized” unit. A stochastic model is developed to elucidate the mechanism behind this coarsening behavior of Pb islands. The distinct evolution of the islands with different heights is correctly predicted, and the size fluctuations of islands and the sudden death behavior observed in island coarsening are also recovered. The key ingredients are incorporation of accurate non-Gaussian statistics of the size fluctuations and also accounting for size changes in large quantized bursts

Influence of Quantum Size Effects on Island Coarsening

DOI:10.1103/PhysRevLett.96.10610 http://prl.aps.org/pdf/PRL/v96/i10/e106105Surface x-ray scattering and scanning-tunneling microscopy experiments reveal novel coarsening behavior of Pb nanocrystals grown on Si 111 - 7 7 . It is found that quantum size effects lead to the breakdown of the classical Gibbs-Thomson analysis. This is manifested by the lack of scaling of the island densities. In addition, island decay times are orders of magnitude faster than expected from the classical analysis and have an unusual dependence on the growth flux F (i.e., 1=F). As a result, a highly monodispersed 7-layer island height distribution is found after coarsening if the islands are grown at high rather than low flux rates. These results have important implications, especially at low temperatures, for the controlled growth and self-organization of nanostructures.The Advanced Photon Source is supported by the DOE Office of Basic Energy Sciences, Contract No. W-31-109-Eng-38. The -CAT beam line is supported through Ames Laboratory, operated for the U.S. DOE by Iowa State University under Contract No. W-7405-Eng-82. Research funding was supported, in part, by Ames Laboratory (M. C. T.), Canim Scientific Group (E. H. C.), the Missouri University Research Board, the National Science Foundation DMR-0405742, and the Petroleum Research Fund No. 41792AC10 (P. F. M., C. A. J., C. K.), the Natural Sciences and Engineering Research Council (NSERC) of Canada (C. A. J.), the Center for Nanostructured Materials Technology under 21st Century Frontier R&D Programs of the Ministry of Science and Technology (No. 05K1501-02520), Korea (C. K.)

A sustainable ultra-high strength Fe18Mn3Ti maraging steel through controlled solute segregation and α-Mn nanoprecipitation

The enormous magnitude of 2 billion tons of alloys produced per year demands a change in design philosophy to make materials environmentally, economically, and socially more sustainable. This disqualifies the use of critical elements that are rare or have questionable origin. Amongst the major alloy strengthening mechanisms, a high-dispersion of second-phase precipitates with sizes in the nanometre range is particularly effective for achieving ultra-high strength. Here, we propose an alternative segregation-based strategy for sustainable steels, free of critical elements, which are rendered ultrastrong by second-phase nano-precipitation. We increase the Mn-content in a supersaturated, metastable Fe-Mn solid solution to trigger compositional fluctuations and nano-segregation in the bulk. These fluctuations act as precursors for the nucleation of an unexpected alpha-Mn phase, which impedes dislocation motion, thus enabling precipitation strengthening. Our steel outperforms most common commercial alloys, yet it is free of critical elements, making it a new platform for sustainable alloy design. Recent demands to design alloys in a more sustainable way have discouraged the use of critical elements that are rare. Here the authors demonstrate a segregation-based strategy to produce a sustainable steel, Fe18Mn3Ti, without critical elements while achieving ultrahigh-strength

ВИВЧЕННЯ ДУМКИ ІНОГОРОДНІХ СТУДЕНТІВ ЩОДО ДОСТУПНОСТІ ТА ЯКОСТІ МЕДИЧНОГО ОБСЛУГОВУВАННЯ

Purpose: to identify major health problems related to the availability and quality of health care for nonresident students, find ways and solutions to these problems. Materials and Methods. An anonymous sociological survey by questioning 100 nonresident students of III-VI years of study in Danylo Halytskyi Lviv National Medical University was conducted. Results. Medical care for nonresident students causes many problems: preference for deterioration of well-being not for professional help of doctors, but for other alternative options (colleagues’ advice, relatives, acquaintances, searching for information on the Internet), unfavourable attitude of non-resident students to medical advice, unwillingness to consult them or provide other types of medical care. It was found out that a greater number of nonresident students (57±5.0) % in case of deterioration in their well-being appeal to their relatives for help, (30±4.6) % search for similar symptoms on the Internet, which leads to the occurrence of complications. (81±3.9) % of nonresident students signed a declaration at the place of residence before entering an educational institution, which can cause difficulties when they need to obtain medical care because of their distant location. Only (42±4.9) % of respondents appeal to medical institutions for the prevention of diseases, periodic examination, which leads to the identification only later stages of diseases, sometimes the terminal ones. To improve the medical care of non-resident students, it is necessary to carry out sanitary and educational work, weeks of prevention of the most common and dangerous diseases in educational institutions. Conclusions. Propaganda of consulting the general practitioners in case of deterioration of well-being will help to make the health of nonresident students better, reduce the morbidity among them.Мета: виявити основні проблеми у сфері охорони здоров’я, що стосуються доступності та якості медичного обслуговування іногородніх студентів, пошук методів та способів вирішення цих проблем. Матеріали і методи. Проведено анонімне соціологічне опитування методом анкетування 100 іногородніх студентів ІІІ–VІ курсів Львівського національного медичного університету імені Данила Галицького. Результати. Медичне обслуговування іногородніх студентів зумовлює багато проблем: віддають перевагу при погіршенні самопочуття альтернативним варіантам допомоги (поради колег, родичів, знайомих, пошук інформації в мережі «Інтернет»), а не професійній допомозі лікарів; неприязне ставлення з боку медичного персоналу до іногородніх студентів; небажання консультувати їх чи надавати інші види медичної допомоги. Виявлено, що більшість іногородніх студентів (57,0±5,0) % у разі погіршення самопочуття звертається за медичною допомогою до родичів, (30,0±4,6) % – шукають аналогічні симптоми захворювання в мережі «Інтернет», що призводить до виникнення ускладнень. Більшість (81,0±3,9) % іногородніх студентів підписала декларацію за місцем проживання ще до вступу в навчальний заклад, це може зумовлювати труднощі при отриманні медичної допомоги через віддалене їх розташування. Тільки (42,0±4,9) % опитаних звертаються у лікувально-профілактичні заклади з метою профілактики захворювань, періодичного обстеження, що призводить до виявлення хвороб на пізніх термінах, іноді вже у термінальній стадії. Для удосконалення медичного обслуговування іногородніх студентів необхідно проводити санітарно-просвітню роботу, тижні профілактики найбільш поширених та небезпечних захворювань у навчальних закладах

Results of surgical treatment in patients, suffering diabetes mellitus and chronic critical ischemia of lower extremity, taking into account the data of intraoperative debitometry

Objective. To analyze the results of surgical treatment of patients, suffering diabetes mellitus, ischemic form of diabetic foot syndrome and chronic critical ischemia of the lower extremity, caused by stenotic-occlusive affection of femoral arterial and popliteo-tibial segments, taking into account the data of intraoperative debitometry. Materials and metods. Results of surgical treatment were analyzed in 67 patients, suffering diabetes mellitus Type II, ischemic form of diabetic foot syndrome and chronic critical ischemia of the lower extremity, caused by stenotic-occlusive affection of femoral arterial and popliteo-tibial segments in 1 and 12 mo. In all the patients a femoro-popliteal shunting without intervention on the popliteo-tibial segment was performed. In accordance to the results obtained during intraoperative debitometry, the patients were distributed into three Groups: Group I - 22 patients with the shunt debit more than 60 ml/min, Group II - 25 patients with the shunt debit 30-60 ml/min, and Group III - 20 patients with the shunt debit lesser than 30 ml/min. In thrombosis of primary zone of arterial reconstruction a reoperation was conducted - a hybrid arterial reconstruction of the popliteo-tibial (thrombectomy from shunt and the balloon angioplasty) segment arteries. Results. In a Group I (n=22) a primary passability of the arterial reconstruction zone in 1mo was observed in 20 (90.9%), and in 12 mo - in 17 (77.3%) patients; in Group II (n=25) - accordingly, in 19 (76%) and 14 (56%) patients; in Group III (n=20) - accordingly, in 9 (45%) and 4 (20%). Thronbosis in the arterial reconstruction zone was diagnosed during a year in 32 patients, of them during first month after primary shunting - in 19 (59.4%), during further 11 mo - in 13 (40.6%) patients. After reoperation for thrombosis of the arterial reconstruction zone, consisting of a hybrid arterial reconstruction, secondary passability of the arterial reconstruction zone during 12 mo was observed in 24 (75%) of 32 patients. While restoration of outflow from popliteal artery into one tibial artery (n=23) during 12 mo a rethrombosis of the arterial reconstructive zone have occurred in 7 patients, secondary passability of the arterial reconstruction zone during 12 mo was observed in 16 (69.6%) patients. While restoration of outflow from popliteal artery into two tibial arteries (n=9) during 12 mo rethrombosis of the arterial reconstruction zone have occurred in 1 patient, secondary passability of the arterial reconstruction zone during 12 mo was observed in 8 (88.9%) patients. Conclusion. In combined stenotic-occlusive affection of femoral arterial segment and arteries of popliteo-tibial segment the isolated restoration of passability and femoral arterial segment without intervention on arteries of popliteo-tibial segment necessitates taking into account the intraoperative debitometry data with determination of the shunt debit constitutes an effective diagnostic method, the data of which may help to adjust a differentiated approach to tactics of surgical treatment in patients, suffering diabetes mellitus, chronic critical ischemia of the lower extremity, caused by stenotic-occlusive affection of femoral arterial segment and arteries of popliteo-tibial segment. The shunt debit bordering value, in presence of which the isolated restoration of the femoral arterial segment passability is possible, constitutes the indices higher than 60 ml/min, further intervention on the popliteo-tibial segment arteries is indicated only in the patients with the shunt thrombosis; while in the shunt debit 30-60 ml/min a reconstruction stage of the popliteo-tibial segment arteries after restoration of the femoral arterial segment passability may be postponed and performed on second stage of the procedure; while the shunt debit lesser than 30 ml/min - a simultaneous reconstruction of femoral segment and of the popliteo-tibial arteries, using performance of a hybrid arterial reconstruction, is necessary. The last is effective method of restoration of blood circulation in patients, suffering diabetes mellitus and chronic critical ischemia of the lower extremity, caused by stenotic-occlusive affection of femoral arterial segment and arteries of popliteo-tibial segment, and in accordance to the results adduced (index of the arterial reconstruction zone passability during 12 mo have constituted 75%) do not differ trustworthily from result of reconstruction of arterial segment in patients of Group I: the shunt debit more than 60 ml/min, while index of the arterial reconstruction zone passability during 12 mo constitutes 77.3% (p>0.05). While thrombosis of primary zone of arterial reconstruction the addition of thrombectomy from the shunt by restoration of the main blood flow from popliteal into two tibial arteries, using the balloon angioplasty, demonstrates a trustworthy best index of secondary passability of the arterial reconstruction zone in 12 mo - 88.9%, comparing with index of secondary passability of the arterial reconstruction zone in 12 mo after restoration of the main blood flow from popliteal artery into one tibial artery - 69.6% (p< 0.05)

Visualizing landscapes of the superconducting gap in heterogeneous superconductor thin films: geometric influences on proximity effects

The proximity effect is a central feature of superconducting junctions as it underlies many important applications in devices and can be exploited in the design of new systems with novel quantum functionality. Recently, exotic proximity effects have been observed in various systems, such as superconductor-metallic nanowires and graphene-superconductor structures. However, it is still not clear how superconducting order propagates spatially in a heterogeneous superconductor system. Here we report intriguing influences of junction geometry on the proximity effect for a 2D heterogeneous superconductor system comprised of 2D superconducting islands on top of a surface metal. Depending on the local geometry, the superconducting gap induced in the surface metal region can either be confined to the boundary of the superconductor, in which the gap decays within a short distance (~ 15 nm), or can be observed nearly uniformly over a distance of many coherence lengths due to non-local proximity effects.Comment: 17 pages, 4 figure

Prefrontal Corticotropin-Releasing Factor (CRF) Neurons Act Locally to Modulate Frontostriatal Cognition and Circuit Function.

The PFC and extended frontostriatal circuitry support higher cognitive processes that guide goal-directed behavior. PFC-dependent cognitive dysfunction is a core feature of multiple psychiatric disorders. Unfortunately, a major limiting factor in the development of treatments for PFC cognitive dysfunction is our limited understanding of the neural mechanisms underlying PFC-dependent cognition. We recently demonstrated that activation of corticotropin-releasing factor (CRF) receptors in the caudal dorsomedial PFC (dmPFC) impairs higher cognitive function, as measured in a working memory task. Currently, there remains much unknown about CRF-dependent regulation of cognition, including the source of CRF for cognition-modulating receptors and the output pathways modulated by these receptors. To address these issues, the current studies used a viral vector-based approach to chemogenetically activate or inhibit PFC CRF neurons in working memory-tested male rats. Chemogenetic activation of caudal, but not rostral, dmPFC CRF neurons potently impaired working memory, whereas inhibition of these neurons improved working memory. Importantly, the cognition-impairing actions of PFC CRF neurons were dependent on local CRF receptors coupled to protein kinase A. Additional electrophysiological recordings demonstrated that chemogenetic activation of caudal dmPFC CRF neurons elicits a robust degradation of task-related coding properties of dmPFC pyramidal neurons and, to a lesser extent, medium spiny neurons in the dorsomedial striatum. Collectively, these results demonstrate that local CRF release within the caudal dmPFC impairs frontostriatal cognitive and circuit function and suggest that CRF may represent a potential target for treating frontostriatal cognitive dysfunction