Demonstration and imaging of cryogenic magneto-thermoelectric cooling in a van der Waals semimetal.

Attaining viable thermoelectric cooling at cryogenic temperatures is of considerable fundamental and technological interest for electronics and quantum materials applications. In-device temperature control can provide more efficient and precise thermal environment management compared with conventional global cooling. The application of a current and perpendicular magnetic field gives rise to cooling by generating electron-hole pairs on one side of the sample and to heating due to their recombination on the opposite side, which is known as the Ettingshausen effect. Here we develop nanoscale cryogenic imaging of the magneto-thermoelectric effect and demonstrate absolute cooling and an Ettingshausen effect in exfoliated WTe2 Weyl semimetal flakes at liquid He temperatures. In contrast to bulk materials, the cooling is non-monotonic with respect to the magnetic field and device size. Our model of magneto-thermoelectricity in mesoscopic semimetal devices shows that the cooling efficiency and the induced temperature profiles are governed by the interplay between sample geometry, electron-hole recombination length, magnetic field, and flake and substrate heat conductivities. The observations open the way for the direct integration of microscopic thermoelectric cooling and for temperature landscape engineering in van der Waals devices.

Direct observation of vortices in an electron fluid.

Vortices are the hallmarks of hydrodynamic flow. Strongly interacting electrons in ultrapure conductors can display signatures of hydrodynamic behaviour, including negative non-local resistance1-4, higher-than-ballistic conduction5-7, Poiseuille flow in narrow channels8-10 and violation of the Wiedemann-Franz law11. Here we provide a visualization of whirlpools in an electron fluid. By using a nanoscale scanning superconducting quantum interference device on a tip12, we image the current distribution in a circular chamber connected through a small aperture to a current-carrying strip in the high-purity type II Weyl semimetal WTe2. In this geometry, the Gurzhi momentum diffusion length and the size of the aperture determine the vortex stability phase diagram. We find that vortices are present for only small apertures, whereas the flow is laminar (non-vortical) for larger apertures. Near the vortical-to-laminar transition, we observe the single vortex in the chamber splitting into two vortices; this behaviour is expected only in the hydrodynamic regime and is not anticipated for ballistic transport. These findings suggest a new mechanism of hydrodynamic flow in thin pure crystals such that the spatial diffusion of electron momenta is enabled by small-angle scattering at the surfaces instead of the routinely invoked electron-electron scattering, which becomes extremely weak at low temperatures. This surface-induced para-hydrodynamics, which mimics many aspects of conventional hydrodynamics including vortices, opens new possibilities for exploring and using electron fluidics in high-mobility electron systems.

Treatment of severe traumatic brain injury in German pediatric intensive care units-a survey of current practice.

PURPOSE: German pediatric guidelines for severe traumatic brain injury (TBI) management expired in 2011. Thus, divergent evidence-based institutional protocols are predominantly being followed. We performed a survey of current Pediatric Intensive Care Unit (PICU) management of isolated severe TBI in Germany to reveal potential varying practices. METHODS: Seventy German PICUs were invited to join an anonymous online survey from February to May 2017. Twenty-nine participants (41.4%) successfully completed the survey (17 university hospitals and 12 district hospitals). The majority of items were polar (yes/no) or scaled (e.g., never - always). Main topics were imaging, neurosurgery, neuromonitoring, adjuvant therapy, and medication. Severity of TBI was defined via Glasgow Coma Scale. RESULTS: The majority of respondents (93.1%) had internal TBI standards, and patients were mainly administered to interdisciplinary trauma units. The use of advanced neuromonitoring techniques, intracranial hypertension management, and drug treatment differed between PICUs. Routine administration of hypertonic saline in TBI-associated cerebral edema was performed by 3.4%, while it was never an option for 31.0% of the participants. Prophylactic anticonvulsive therapy was restrictively performed. If indicated, the main anticonvulsive drugs used were phenobarbital and levetiracetam. Neuroendocrine follow-up was recommended/performed by 58.6% of the PICUs. CONCLUSIONS: This survey provides an overview of the current PICU practices of isolated severe TBI management in Germany and demonstrates a wide instrumental and therapeutical range, revealing an unmet need for the revised national guideline and further (international) clinical trials for the treatment of severe TBI in pediatrics.

[Chronological age of patients with Turner syndrome at diagnosis]. / Chronologisches Alter von Mädchen mit Ullrich-Turner-Syndrom bei Diagnosestellung.

BACKGROUND: Phenotypically, Turner syndrome (TS) is characterized by great variability, with short stature being the most constant incidence. Growth hormone therapy can achieve a significant improvement in the final size of the patient, which, however, is highly dependent on early diagnosis of the disease. The objective of our study was to determine the age at which the affected girls among our patient collective were diagnosed with TS and which symptoms were indicative. PATIENTS: The time of diagnosis and the reason for karyotyping were retrospectively determined for 117 girls with TS, who had presented at the Hospital for Children and Adolescents of the University of Erlangen, Germany, in the period between 1980 and 2002. RESULTS: Seven children were prenatally diagnosed with TS by amniocentesis and 27 children were postnatally diagnosed with the disease. TS was diagnosed during infancy in 10 children (median 0.2 years, range 0.1-0.9 yrs.), during early childhood in 4 children (median 1.7 years, range 1.1-2.2 yrs.), and during preschool age in 11 girls (median 5 years, range 4-5.8 yrs.). In 58 girls, i.e. almost 50%, TS was diagnosed after the age of 6: n=27 between the age of 6 and 11 (median 8.9 years, range 6.1-10.8 yrs.) and n=31 after the age of 11 (median 13 years, range 11.1-17 yrs.). Lymphedema (26 cases), dysmorphic symptoms (14 cases), and heart failures (6 cases) were the reason for karyotyping performed at birth and during infancy. With increasing age, TS was diagnosed based on short stature (66 of 73 cases). CONCLUSIONS: The available data shows that the majority of the patients were diagnosed late and that short stature was the most important diagnostic symptom.

[Attempted suicide with L-thyroxine in an adolescent girl]. / Intoxikation mit L-Thyroxin in suizidaler Absicht bei einer Jugendlichen.

BACKGROUND: Attempted suicide with l-thyroxine (LT4) is very rare, only being published in some case reports concerning young women. Experiences in the management of LT4 intoxication have already been made because overdosage in infants occurs more often. Guidelines and recommendations depend on the quantity of LT4 that has been ingested. PATIENT: A 17-year-old girl presented to the pediatric emergency department after intentional ingestion of 20 mg of LT4 20 hours prior to admission. Anamnestically she had increased the thyroxine dose rate up to 800 microg per day during the previous 4 months in order to obtain loss of weight. In spite of massive overdosage and extremely high serum thyroxine levels (fT4 794 pg/ml, TSH suppressed) the girls showed low symptoms and a mild clinical course. Because of tachycardia, hyperhidrosis and muscle tremor propranolol was applied. During the following 22 days fT4 levels returned to normal range and the adolescent was remitted to the outpatient clinic of the department of psychiatry. Whereas patients with graves disease and thyreotoxicosis present with severe symptoms our patient showed a mild clinical course in spite of having extremely high fT4 levels. CONCLUSIONS: The reasons are ambiguous. A possible answer could be an adaptation in higher fT4 levels in cause of the reported chronic LT4 overdosage.

Spontaneous prolactin secretion in growth hormone-deficient children.

OBJECTIVE: To establish the spontaneous nocturnal prolactin (PRL) release in relation to growth hormone (GH)-deficient children and idiopathic short-stature children (ISS). METHODS: A total of 32 prepubertal children (11 girls, 21 boys) aged between 3 and 12 years were studied retrospectively and sorted according to diagnosis: idiopathic GH deficiency (GHD, n = 9), neurosecretory deficiency of GH secretion (NSD, n = 10) and ISS (n = 13). Nocturnal spontaneous hormone secretion was studied by intermittent venous sampling. Secretion profiles and copulsatility were analyzed using Pulsar and AnCoPuls software. RESULTS: (median, range in mug/l): Children with GHD and NSD had significantly lower GH and area-under-the-curve (AUC) levels than normal children (p < 0.001), whereas ISS children showed normal values. In contrast, prolactin levels were significantly higher (p < 0. 05) in children with GHD and NSD (11.1, 4.9 - 13.0 and 10.3, 8. 8 - 19. 6, respectively) compared to the ISS children (8.0, 4.9 - 13.0). In addition, prolactin AUC and peak height were higher (p < 0.05) in GH-deficient patients, whereas all other secretion parameters were the same. Correlation and copulsatility analysis revealed no evidence for a direct relation between PRL and GH secretion. CONCLUSIONS: PRL secretion is significantly higher in children with GHD and NSD compared to ISS children but PRL and GH show no copulsatile secretion pattern.