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1.
Phys Rev Lett ; 123(2): 027205, 2019 Jul 12.
Artículo en Inglés | MEDLINE | ID: mdl-31386536

RESUMEN

We report on negative thermal expansion (NTE) in the high-field, half-magnetization plateau phase of the frustrated magnetic insulator CdCr_{2}O_{4}. Using dilatometry, we precisely map the phase diagram at fields of up to 30 T and identify a strong NTE associated with the collinear half-magnetization plateau for B>27 T. The resulting phase diagram is compared with a microscopic theory for spin-lattice coupling, and the origin of the NTE is identified as a large negative change in magnetization with temperature, coming from a nearly localized band of spin excitations in the plateau phase. These results provide useful guidelines for the discovery of new NTE materials.

2.
Phys Rev Lett ; 121(25): 256602, 2018 Dec 21.
Artículo en Inglés | MEDLINE | ID: mdl-30608835

RESUMEN

We report a study of quantum oscillations in the high-field magnetoresistance of the nodal-line semimetal HfSiS. In the presence of a magnetic field up to 31 T parallel to the c axis, we observe quantum oscillations originating both from orbits of individual electron and hole pockets, and from magnetic breakdown between these pockets. In particular, we reveal a breakdown orbit enclosing one electron and one hole pocket in the form of a "figure of eight," which is a manifestation of Klein tunneling in momentum space, although in a regime of partial transmission due to the finite separation between the pockets. The observed very strong dependence of the oscillation amplitude on the field angle and the cyclotron masses of the orbits are in agreement with the theoretical predictions for this novel tunneling phenomenon.

3.
Nat Commun ; 8(1): 1337, 2017 11 07.
Artículo en Inglés | MEDLINE | ID: mdl-29116084

RESUMEN

When a magnetic field confines the carriers of a Fermi sea to their lowest Landau level, electron-electron interactions are expected to play a significant role in determining the electronic ground state. Graphite is known to host a sequence of magnetic field-induced states driven by such interactions. Three decades after their discovery, thermodynamic signatures of these instabilities are still elusive. Here we report the detection of these transitions with sound velocity measurements. The evolution of elastic constant anomalies with temperature and magnetic field allows to draw a detailed phase diagram which shows that the ground state evolves in a sequence of thermodynamic phase transitions. Our analysis indicates that the electron-electron interaction is not the sole driving force of these transitions and that lattice degrees of freedom play an important role.

4.
Rev Sci Instrum ; 88(8): 083903, 2017 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-28863703

RESUMEN

For the characterization of novel quantum phases of matter, it is often required to study materials under multi-extreme conditions, in particular down to very low temperatures and in very high magnetic fields. We developed the world's smallest high-resolution capacitive dilatometer suitable for temperatures down to 10 mK and usage in high magnetic fields up to 37.5 T. Despite the extreme miniaturization, the capacitive dilatometer can resolve length changes down to 0.01 Å. This is an unprecedented resolution in a capacitive dilatometer of this compact size. Many cryogenic devices have limited space. Due to the extremely reduced cell size (3 cm3, 12 g), implementation or new applications in many of these sample space lacking devices are now possible. As an important example, the minute device can now be rotated in any standard cryostat, including dilution refrigerators or the commercial physical property measurement system. The present super compact design provides also for high resolution thermal expansion and magnetostriction measurements in a 15.2 mm diameter tube, enabling its use in the 32 mm bore, 37.5 T Bitter magnet at the High Field Magnet Laboratory in Nijmegen down to a temperature of 300 mK.

5.
Pneumologie ; 71(9): 580-586, 2017 Sep.
Artículo en Alemán | MEDLINE | ID: mdl-28449136

RESUMEN

Background and objectives Alpha-2 Macroglobulin (A2M) is a plasma protein with proteolytic effects on many proteases. In patients with an inborn alpha-1 antitrypsin deficiency (AATD) the homeostasis between proteases and antiproteases is disturbed. The aim of this study was to compare the levels of AAT and A2 M in patients and controls. We hypothesized that in patients with AATD A2 M levels are elevated. Methods Patients with AATD (polymorphism Pi*ZZ, Pi*SZ, Pi*MZ and rare gene variants) as well as healthy volunteers (Pi*MM) were tested for A2 M and AAT levels. The concentration of the proteins was measured by nephelometry. The polymorphisms Pi*Z and Pi*S were detected by polymerase chain reaction (PCR), the rare genetic variants were identified by sequencing. Results In our study, a total of 291 individuals were included. It could be shown that a significant increase in A2 M levels in the serum could be observed in the presence of a gene polymorphism (Pi*ZZ) and an alpha-1 antitrypsin serum level < 50 mg/dl compared to the healthy volunteers. Conclusions In this study, an inverse correlation between the serum levels of AAT and A2 M was found in the presence of a gene polymorphism (Pi*ZZ). Further studies are necessary to elucidate the clinical significance of increased A2 M serum levels in patients with severe AAT deficiency Pi*ZZ and rare gene variants whose AAT serum level is < 50 mg/dl.


Asunto(s)
alfa 2-Macroglobulinas Asociadas al Embarazo/metabolismo , Deficiencia de alfa 1-Antitripsina/sangre , Estudios de Cohortes , Análisis Mutacional de ADN , Femenino , Variación Genética/genética , Homeostasis/fisiología , Humanos , Masculino , Persona de Mediana Edad , Polimorfismo Genético , Enfermedad Pulmonar Obstructiva Crónica/sangre , Enfermedad Pulmonar Obstructiva Crónica/genética , Valores de Referencia , alfa 1-Antitripsina/sangre , Deficiencia de alfa 1-Antitripsina/genética
6.
Phys Rev Lett ; 117(25): 256601, 2016 Dec 16.
Artículo en Inglés | MEDLINE | ID: mdl-28036219

RESUMEN

We report a high-field magnetotransport study of an ultrahigh mobility (µ[over ¯]≈25×10^{6} cm^{2} V^{-1} s^{-1}) n-type GaAs quantum well. We observe a strikingly large linear magnetoresistance (LMR) up to 33 T with a magnitude of order 10^{5}% onto which quantum oscillations become superimposed in the quantum Hall regime at low temperature. LMR is very often invoked as evidence for exotic quasiparticles in new materials such as the topological semimetals, though its origin remains controversial. The observation of such a LMR in the "simplest system"-with a free electronlike band structure and a nearly defect-free environment-excludes most of the possible exotic explanations for the appearance of a LMR and rather points to density fluctuations as the primary origin of the phenomenon. Both, the featureless LMR at high T and the quantum oscillations at low T follow the empirical resistance rule which states that the longitudinal conductance is directly related to the derivative of the transversal (Hall) conductance multiplied by the magnetic field and a constant factor α that remains unchanged over the entire temperature range. Only at low temperatures, small deviations from this resistance rule are observed beyond ν=1 that likely originate from a different transport mechanism for the composite fermions.

7.
Science ; 353(6299): 575-9, 2016 Aug 05.
Artículo en Inglés | MEDLINE | ID: mdl-27493182

RESUMEN

Chirality is a fundamental property of electrons with the relativistic spectrum found in graphene and topological insulators. It plays a crucial role in relativistic phenomena, such as Klein tunneling, but it is difficult to visualize directly. Here, we report the direct observation and manipulation of chirality and pseudospin polarization in the tunneling of electrons between two almost perfectly aligned graphene crystals. We use a strong in-plane magnetic field as a tool to resolve the contributions of the chiral electronic states that have a phase difference between the two components of their vector wave function. Our experiments not only shed light on chirality, but also demonstrate a technique for preparing graphene's Dirac electrons in a particular quantum chiral state in a selected valley.

8.
Nervenarzt ; 87(4): 426-32, 2016 Apr.
Artículo en Alemán | MEDLINE | ID: mdl-26818024

RESUMEN

BACKGROUND: There are a variety of intensive care therapies in the treatment of malignant middle cerebral artery infarction (MMI) besides hemicraniectomy (HC), the only treatment with proven efficacy. It is, however, not known how HC and conservative treatments are utilized in German hospitals, Furthermore, data on the care-situation of patients with MMI in Germany is scarce. METHODS: An anonymous questionnaire was sent to 297 neurological and 133 neurosurgical hospitals in Germany. RESULTS: The Response rate was 24,7%. Most respondents indicated personal experience in the treatment of MMI (83,3%). HC is usually performed early on site (83,3%). Indication to HC is confirmed on a high level of hierarchy and profession using clinical and radiological criteria in 78,2% of hospitals. Inherent standardized treatment protocols are established in 70,8% of hospitals. Patients are treated on an intensive care unit in 74,5% of hospitals after DHC and in 42,5% of hospitals under non-surgical treatment. Intracranial pressure monitoring is not performed on a regular basis. Differing opinions were observed concerning diagnosis and treatment of MMI without recognizable consensus. CONCLUSION: Basically, structural requirements for the treatment of MMI exist in the participating hospitals. Heterogeneity in the treatment of MMI is striking. The implementation of treatment protocols and adherence to guidelines are desirable steps to optimize treatment.


Asunto(s)
Craniectomía Descompresiva/estadística & datos numéricos , Hospitales/estadística & datos numéricos , Infarto de la Arteria Cerebral Media/epidemiología , Infarto de la Arteria Cerebral Media/cirugía , Neurología/estadística & datos numéricos , Pautas de la Práctica en Medicina/estadística & datos numéricos , Anciano , Competencia Clínica/estadística & datos numéricos , Alemania/epidemiología , Hospitalización/estadística & datos numéricos , Humanos , Infarto de la Arteria Cerebral Media/diagnóstico , Persona de Mediana Edad , Prevalencia , Estudios Retrospectivos
9.
Internist (Berl) ; 56(2): 121-6, 2015 Feb.
Artículo en Alemán | MEDLINE | ID: mdl-25636954

RESUMEN

BACKGROUND: Obesity is an important risk factor for the development of heart failure. DIAGNOSTICS: In normotensive obese patients, a reduced peripheral resistance is typically observed and is accompanied by an increased fluid volume and an increase in cardiac work, resulting in hypertrophy and diastolic heart failure, which can be visualized with echocardiography. However, in the presence of arterial hypertension cardiac geometry is not different to hypertensive heart disease without obesity. Furthermore, the typical changes found with obesity, such as reduced peripheral resistance and increased blood volume, are no longer present. Obstructive sleep apnea (OSA) is very common in obesity and warrants screening but levels of the heart failure marker N-terminal pro-brain natriuretic peptide (NT-ProBNP) might be misleading as the values are lower in obesity than in normal weight controls. THERAPY: Body weight reduction is advisable but difficult to achieve and much more difficult to maintain. Furthermore, diet and exercise has not been proven to enhance life expectancy in obesity. However, with bariatric surgery, long-term weight reduction can be achieved and mortality can be reduced. CONCLUSIONS: With effective weight loss and improved clinical outcome after bariatric surgery, treatment of obesity has shifted much more into focus. Regardless of technical challenges in the work-up of obese patients, clinical symptoms suggestive of cardiac disorders warrant prompt investigation with standard techniques following recommendations as established for normal weight patients.


Asunto(s)
Cirugía Bariátrica/métodos , Insuficiencia Cardíaca/etiología , Insuficiencia Cardíaca/prevención & control , Obesidad/complicaciones , Obesidad/terapia , Dietoterapia/métodos , Terapia por Ejercicio/métodos , Insuficiencia Cardíaca/diagnóstico , Humanos , Obesidad/diagnóstico , Factores de Riesgo , Resultado del Tratamiento
10.
Animal ; 8(4): 643-9, 2014 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-24461060

RESUMEN

In the context of assessing the impact of management and environmental factors on animal health, behaviour or performance it has become increasingly important to conduct (epidemiological) studies in the field. Hence, the number of investigated farms per study is considerably high so that numerous observers are needed for investigation. In order to maintain the quality and validity of study results calibration meetings where observers are trained and the current level of agreement is assessed have to be conducted to minimise the observer effect. When study animals were rated independently by the same observers by a categorical variable the exclusion test can be performed to identify disagreeing observers. This statistical test compares for each variable and each observer the observer-specific agreement with the overall agreement among all observers based on kappa coefficients. It accounts for two major challenges, namely the absence of a gold-standard observer and different data type comprising ordinal, nominal and binary data. The presented methods are applied on a reliability study to assess the agreement among eight observers rating welfare parameters of laying hens. The degree to which the observers agreed depended on the investigated item (global weighted kappa coefficients: 0.37 to 0.94). The proposed method and graphical description served to assess the direction and degree to which an observer deviates from the others. It is suggested to further improve studies with numerous observers by conducting calibration meetings and accounting for observer bias.


Asunto(s)
Crianza de Animales Domésticos/estadística & datos numéricos , Variaciones Dependientes del Observador , Animales , Reproducibilidad de los Resultados
11.
Proc Natl Acad Sci U S A ; 110(9): 3282-6, 2013 Feb 26.
Artículo en Inglés | MEDLINE | ID: mdl-23401538

RESUMEN

Capacitance measurements provide a powerful means of probing the density of states. The technique has proved particularly successful in studying 2D electron systems, revealing a number of interesting many-body effects. Here, we use large-area high-quality graphene capacitors to study behavior of the density of states in this material in zero and high magnetic fields. Clear renormalization of the linear spectrum due to electron-electron interactions is observed in zero field. Quantizing fields lead to splitting of the spin- and valley-degenerate Landau levels into quartets separated by interaction-enhanced energy gaps. These many-body states exhibit negative compressibility but the compressibility returns to positive in ultrahigh B. The reentrant behavior is attributed to a competition between field-enhanced interactions and nascent fractional states.

12.
Neurology ; 76(2): 159-65, 2011 Jan 11.
Artículo en Inglés | MEDLINE | ID: mdl-21148118

RESUMEN

BACKGROUND: Contemporaneous data on variations in outcome after first-ever-lifetime stroke between European populations are lacking. We compared differences in case fatality rates, functional outcome, and living conditions 3 months after stroke within the European Registers of Stroke Collaboration. METHODS: Population-based stroke registers were established in France (Dijon), Italy (Sesto Fiorentino), Lithuania (Kaunas), the United Kingdom (London), Spain (Menorca), and Poland (Warsaw). All patients with first-ever-lifetime stroke of all age groups from the source population (1,087,048 inhabitants) were included. Data collection took part between 2004 and 2006. The study investigated population variations in outcome at 3 months (death, institutionalization due to stroke, or Barthel Index below 12 points) using multivariable logistic regression analyses adjusted for age, sex, stroke severity, stroke subtype, and comorbidities. RESULTS: A total of 2,034 patients with first-ever-lifetime stroke were included. Median age was 73 years, 52% were female. The mean weighted cumulative risk of death was 21.8% (95% confidence interval 20.0 to 23.6) with a 3-fold variation across populations. The weighted proportion of poor outcome was 41.3% (95% confidence interval 39.0 to 43.7) with a 2-fold variation across populations. CONCLUSION: More than 40% of patients had a poor outcome, defined as being dead, dependent, or institutionalized 3 months after stroke. Substantial outcome variations were found between populations that were explained by case mix variables in this analysis, yet a trend toward a higher risk of poor outcome was present in Kaunas.


Asunto(s)
Institucionalización/estadística & datos numéricos , Sistema de Registros , Accidente Cerebrovascular/mortalidad , Accidente Cerebrovascular/fisiopatología , Factores de Edad , Anciano , Anciano de 80 o más Años , Intervalos de Confianza , Progresión de la Enfermedad , Femenino , Francia/epidemiología , Humanos , Italia/epidemiología , Lituania/epidemiología , Masculino , Persona de Mediana Edad , Polonia/epidemiología , Análisis de Regresión , Factores de Riesgo , Índice de Severidad de la Enfermedad , Factores Sexuales , España/epidemiología , Accidente Cerebrovascular/diagnóstico , Factores de Tiempo , Reino Unido/epidemiología
13.
Phys Rev Lett ; 105(2): 026804, 2010 Jul 09.
Artículo en Inglés | MEDLINE | ID: mdl-20867726

RESUMEN

Magnetotransport measurements on a high-mobility electron bilayer system formed in a wide GaAs quantum well reveal vanishing dissipative resistance under continuous microwave irradiation. Profound zero-resistance states (ZRS) appear even in the presence of additional intersubband scattering of electrons. We study the dependence of photoresistance on frequency, microwave power, and temperature. Experimental results are compared with a theory demonstrating that the conditions for absolute negative resistivity correlate with the appearance of ZRS.

15.
Artículo en Alemán | MEDLINE | ID: mdl-9101861

RESUMEN

Documentation is becoming an ever more time-consuming task due to the need to document increasing ICU productivity, quality management and cost-assessment data. Automatic charting of on-line monitoring data, therapeutic-device data, clinical laboratory data, microbiological data, radiological data and other data reduces documentation time significantly. One of the major advantages of PDMS in the SICU is the quality of the documentation and with better documentation the therapist is able to improve the quality of care. Not only the physician, but also nurses and physiotherapists are able to benefit from these advantages. Our concept, SURGIC (Department of Surgery, University Regensburg, Germany, Intensive Care), stands for: widely automated documentation, work orientation, including physicians, nurses' and physiotherapists' tasks, minimal dataset for simple use and perfect overview, costs assessments, scientific dataset, SICU PDMS as a part of the clinical information system, and professional support by a software-house is necessary.


Asunto(s)
Cuidados Críticos , Documentación/métodos , Sistemas de Información en Hospital/organización & administración , Sistemas de Registros Médicos Computarizados/instrumentación , Monitoreo Fisiológico/instrumentación , Complicaciones Posoperatorias/terapia , Sistemas de Computación , Análisis Costo-Beneficio , Cuidados Críticos/economía , Recolección de Datos , Documentación/economía , Sistemas de Información en Hospital/economía , Humanos , Sistemas de Registros Médicos Computarizados/economía , Monitoreo Fisiológico/economía , Grupo de Atención al Paciente , Complicaciones Posoperatorias/economía , Programas Informáticos
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