462 research outputs found
Antiferromagnetic CuMnAs multi-level memory cell with microelectronic compatibility
Antiferromagnets offer a unique combination of properties including the radiation and magnetic field hardness, the absence of stray magnetic fields, and the spin-dynamics frequency scale in terahertz. Recent experiments have demonstrated that relativistic spin-orbit torques can provide the means for an efficient electric control of antiferromagnetic moments. Here we show that elementary-shape memory cells fabricated from a single-layer antiferromagnet CuMnAs deposited on a III–V or Si substrate have deterministic multi-level switching characteristics. They allow for counting and recording thousands of input pulses and responding to pulses of lengths downscaled to hundreds of picoseconds. To demonstrate the compatibility with common microelectronic circuitry, we implemented the antiferromagnetic bit cell in a standard printed circuit board managed and powered at ambient conditions by a computer via a USB interface. Our results open a path towards specialized embedded memory-logic applications and ultra-fast components based on antiferromagnets
Skeletal muscle AMPK is not activated during 2 h of moderate intensity exercise at ~65% VO2peak in endurance trained men
Key points: AMP-activated protein kinase (AMPK) is considered a major regulator of skeletal muscle metabolism during exercise. However, we previously showed that, although AMPK activity increases by 8–10-fold during ∼120 min of exercise at ∼65% (Formula presented.) in untrained individuals, there is no increase in these individuals after only 10 days of exercise training (longitudinal study). In a cross-sectional study, we show that there is also a lack of activation of skeletal muscle AMPK during 120 min of cycling exercise at 65% (Formula presented.) in endurance-trained individuals. These findings indicate that AMPK is not an important regulator of exercise metabolism during 120 min of exercise at 65% (Formula presented.) in endurance trained men. It is important that more energy is directed towards examining other potential regulators of exercise metabolism. Abstract: AMP-activated protein kinase (AMPK) is considered a major regulator of skeletal muscle metabolism during exercise. Indeed, AMPK is activated during exercise and activation of AMPK by 5-aminoimidazole-4-carboxyamide-ribonucleoside (AICAR) increases skeletal muscle glucose uptake and fat oxidation. However, we have previously shown that, although AMPK activity increases by 8–10-fold during ∼120 min of exercise at ∼65% (Formula presented.) in untrained individuals, there is no increase in these individuals after only 10 days of exercise training (longitudinal study). In a cross-sectional study, we examined whether there is also a lack of activation of skeletal muscle AMPK during 120 min of cycling exercise at 65% (Formula presented.) in endurance-trained individuals. Eleven untrained (UT; (Formula presented.) = 37.9 ± 5.6 ml.kg−1 min−1) and seven endurance trained (ET; (Formula presented.) = 61.8 ± 2.2 ml.kg−1 min−1) males completed 120 min of cycling exercise at 66 ± 4% (Formula presented.) (UT: 100 ± 21 W; ET: 190 ± 15 W). Muscle biopsies were obtained at rest and following 30 and 120 min of exercise. Muscle glycogen was significantly (P < 0.05) higher before exercise in ET and decreased similarly during exercise in the ET and UT individuals. Exercise significantly increased calculated skeletal muscle free AMP content and more so in the UT individuals. Exercise significantly (P < 0.05) increased skeletal muscle AMPK α2 activity (4-fold), AMPK αThr172 phosphorylation (2-fold) and ACCβ Ser222 phosphorylation (2-fold) in the UT individuals but not in the ET individuals. These findings indicate that AMPK is not an important regulator of exercise metabolism during 120 min of exercise at 65% (Formula presented.) in endurance trained men
Stage of perinatal development regulates skeletal muscle mitochondrial biogenesis and myogenic regulatory factor genes with little impact of growth restriction or cross-fostering
Foetal growth restriction impairs skeletal muscle development and adult muscle mitochondrial biogenesis. We hypothesized that key genes involved in muscle development and mitochondrial biogenesis would be altered following uteroplacental insufficiency in rat pups, and improving postnatal nutrition by cross-fostering would ameliorate these deficits. Bilateral uterine vessel ligation (Restricted) or sham (Control) surgery was performed on day 18 of gestation. Males and females were investigated at day 20 of gestation (E20), 1 (PN1), 7 (PN7) and 35 (PN35) days postnatally. A separate cohort of Control and Restricted pups were cross-fostered onto a different Control or Restricted mother and examined at PN7. In both sexes, peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1α (PGC-1α), cytochrome c oxidase subunits 3 and 4 (COX III and IV) and myogenic regulatory factor 4 expression increased from late gestation to postnatal life, whereas mitochondrial transcription factor A, myogenic differentiation 1 (MyoD), myogenin and insulin-like growth factor I (IGF-I) decreased. Foetal growth restriction increased MyoD mRNA in females at PN7, whereas in males IGF-I mRNA was higher at E20 and PN1. Cross-fostering Restricted pups onto a Control mother significantly increased COX III mRNA in males and COX IV mRNA in both sexes above controls with little effect on other genes. Developmental age appears to be a major factor regulating skeletal muscle mitochondrial and developmental genes, with growth restriction and cross-fostering having only subtle effects. It therefore appears that reductions in adult mitochondrial biogenesis markers likely develop after weaning.<br /
Skeletal muscle AMPK is not activated during 2 h of moderate intensity exercise at ∼65% VO2 peak in endurance trained men
KEY POINTS: AMP-activated protein kinase (AMPK) is considered a major regulator of skeletal muscle metabolism during exercise. However, we previously showed that, although AMPK activity increases by 8-10-fold during ∼120 min of exercise at ∼65% V ̇ O 2 peak in untrained individuals, there is no increase in these individuals after only 10 days of exercise training (longitudinal study). In a cross-sectional study, we show that there is also a lack of activation of skeletal muscle AMPK during 120 min of cycling exercise at 65% V ̇ O 2 peak in endurance-trained individuals. These findings indicate that AMPK is not an important regulator of exercise metabolism during 120 min of exercise at 65% V ̇ O 2 peak in endurance trained men. It is important that more energy is directed towards examining other potential regulators of exercise metabolism. ABSTRACT: AMP-activated protein kinase (AMPK) is considered a major regulator of skeletal muscle metabolism during exercise. Indeed, AMPK is activated during exercise and activation of AMPK by 5-aminoimidazole-4-carboxyamide-ribonucleoside (AICAR) increases skeletal muscle glucose uptake and fat oxidation. However, we have previously shown that, although AMPK activity increases by 8-10-fold during ∼120 min of exercise at ∼65% V ̇ O 2 peak in untrained individuals, there is no increase in these individuals after only 10 days of exercise training (longitudinal study). In a cross-sectional study, we examined whether there is also a lack of activation of skeletal muscle AMPK during 120 min of cycling exercise at 65% V ̇ O 2 peak in endurance-trained individuals. Eleven untrained (UT; V ̇ O 2 peak = 37.9 ± 5.6 ml.kg-1 min-1 ) and seven endurance trained (ET; V ̇ O 2 peak = 61.8 ± 2.2 ml.kg-1 min-1 ) males completed 120 min of cycling exercise at 66 ± 4% V ̇ O 2 peak (UT: 100 ± 21 W; ET: 190 ± 15 W). Muscle biopsies were obtained at rest and following 30 and 120 min of exercise. Muscle glycogen was significantly (P < 0.05) higher before exercise in ET and decreased similarly during exercise in the ET and UT individuals. Exercise significantly increased calculated skeletal muscle free AMP content and more so in the UT individuals. Exercise significantly (P < 0.05) increased skeletal muscle AMPK α2 activity (4-fold), AMPK αThr172 phosphorylation (2-fold) and ACCβ Ser222 phosphorylation (2-fold) in the UT individuals but not in the ET individuals. These findings indicate that AMPK is not an important regulator of exercise metabolism during 120 min of exercise at 65% V ̇ O 2 peak in endurance trained men
Lithic technological responses to Late Pleistocene glacial cycling at Pinnacle Point Site 5-6, South Africa
There are multiple hypotheses for human responses to glacial cycling in the Late Pleistocene, including changes in population size, interconnectedness, and mobility. Lithic technological analysis informs us of human responses to environmental change because lithic assemblage characteristics are a reflection of raw material transport, reduction, and discard behaviors that depend on hunter-gatherer social and economic decisions. Pinnacle Point Site 5-6 (PP5-6), Western Cape, South Africa is an ideal locality for examining the influence of glacial cycling on early modern human behaviors because it preserves a long sequence spanning marine isotope stages (MIS) 5, 4, and 3 and is associated with robust records of paleoenvironmental change. The analysis presented here addresses the question, what, if any, lithic assemblage traits at PP5-6 represent changing behavioral responses to the MIS 5-4-3 interglacial-glacial cycle? It statistically evaluates changes in 93 traits with no a priori assumptions about which traits may significantly associate with MIS. In contrast to other studies that claim that there is little relationship between broad-scale patterns of climate change and lithic technology, we identified the following characteristics that are associated with MIS 4: increased use of quartz, increased evidence for outcrop sources of quartzite and silcrete, increased evidence for earlier stages of reduction in silcrete, evidence for increased flaking efficiency in all raw material types, and changes in tool types and function for silcrete. Based on these results, we suggest that foragers responded to MIS 4 glacial environmental conditions at PP5-6 with increased population or group sizes, 'place provisioning', longer and/or more intense site occupations, and decreased residential mobility. Several other traits, including silcrete frequency, do not exhibit an association with MIS. Backed pieces, once they appear in the PP5-6 record during MIS 4, persist through MIS 3. Changing paleoenvironments explain some, but not all temporal technological variability at PP5-6.Social Science and Humanities Research Council of Canada; NORAM; American-Scandinavian Foundation; Fundacao para a Ciencia e Tecnologia [SFRH/BPD/73598/2010]; IGERT [DGE 0801634]; Hyde Family Foundations; Institute of Human Origins; National Science Foundation [BCS-9912465, BCS-0130713, BCS-0524087, BCS-1138073]; John Templeton Foundation to the Institute of Human Origins at Arizona State Universit
Optical determination of the Néel vector in a CuMnAs thin-film antiferromagnet
Recent breakthroughs in electrical detection and manipulation of antiferromagnets have opened a new avenue in the research of non-volatile spintronic devices.1-10 Antiparallel spin sublattices in antiferromagnets, producing zero dipolar fields, lead to the insensitivity to magnetic field perturbations, multi-level stability, ultrafast spin dynamics and other favorable characteristics which may find utility in fields ranging from magnetic memories to optical signal processing. However, the absence of a net magnetic moment and the ultra-short magnetization dynamics timescales make antiferromagnets notoriously difficult to study by common magnetometers or magnetic resonance techniques. In this paper we demonstrate the experimental determination of the Néel vector in a thin film of antiferromagnetic CuMnAs9,10 which is the prominent material used in the first realization of antiferromagnetic memory chips.10 We employ a femtosecond pump-probe magneto-optical experiment based on magnetic linear dichroism. This table-top optical method is considerably more accessible than the traditionally employed large scale facility techniques like neutron diffraction11 and Xray magnetic dichroism measurements.12-14 This optical technique allows an unambiguous direct determination of the Néel vector orientation in thin antiferromagnetic films utilized in devices directly from measured data without fitting to a theoretical model
Impaired postprandial skeletal muscle vascular responses to a mixed meal challenge in normoglycaemic people with a parent with type 2 diabetes
Aims/hypothesis: Microvascular blood flow (MBF) increases in skeletal muscle postprandially to aid in glucose delivery and uptake in muscle. This vascular action is impaired in individuals who are obese or have type 2 diabetes. Whether MBF is impaired in normoglycaemic people at risk of type 2 diabetes is unknown. We aimed to determine whether apparently healthy people at risk of type 2 diabetes display impaired skeletal muscle microvascular responses to a mixed-nutrient meal.
Methods: In this cross-sectional study, participants with no family history of type 2 diabetes (FH-) for two generations (n = 18), participants with a positive family history of type 2 diabetes (FH+; i.e. a parent with type 2 diabetes; n = 16) and those with type 2 diabetes (n = 12) underwent a mixed meal challenge (MMC). Metabolic responses (blood glucose, plasma insulin and indirect calorimetry) were measured before and during the MMC. Skeletal muscle large artery haemodynamics (2D and Doppler ultrasound, and Mobil-O-graph) and microvascular responses (contrast-enhanced ultrasound) were measured at baseline and 1 h post MMC.
Results: Despite normal blood glucose concentrations, FH+ individuals displayed impaired metabolic flexibility (reduced ability to switch from fat to carbohydrate oxidation vs FH-; p \u3c 0.05) during the MMC. The MMC increased forearm muscle microvascular blood volume in both the FH- (1.3-fold, p \u3c 0.01) and FH+ (1.3-fold, p \u3c 0.05) groups but not in participants with type 2 diabetes. However, the MMC increased MBF (1.9-fold, p \u3c 0.01), brachial artery diameter (1.1-fold, p \u3c 0.01) and brachial artery blood flow (1.7-fold, p \u3c 0.001) and reduced vascular resistance (0.7-fold, p \u3c 0.001) only in FH- participants, with these changes being absent in FH+ and type 2 diabetes. Participants with type 2 diabetes displayed significantly higher vascular stiffness (p \u3c 0.001) compared with those in the FH- and FH+ groups; however, vascular stiffness did not change during the MMC in any participant group.
Conclusions/interpretation: Normoglycaemic FH+ participants display impaired postprandial skeletal muscle macro- and microvascular responses, suggesting that poor vascular responses to a meal may contribute to their increased risk of type 2 diabetes. We conclude that vascular insulin resistance may be an early precursor to type 2 diabetes in humans, which can be revealed using an MMC
Finding 3D motifs in ribosomal RNA structures
The identification of small structural motifs and their organization into larger subassemblies is of fundamental interest in the analysis, prediction and design of 3D structures of large RNAs. This problem has been studied only sparsely, as most of the existing work is limited to the characterization and discovery of motifs in RNA secondary structures. We present a novel geometric method for the characterization and identification of structural motifs in 3D rRNA molecules. This method enables the efficient recognition of known 3D motifs, such as tetraloops, E-loops, kink-turns and others. Furthermore, it provides a new way of characterizing complex 3D motifs, notably junctions, that have been defined and identified in the secondary structure but have not been analyzed and classified in three dimensions. We demonstrate the relevance and utility of our approach by applying it to the Haloarcula marismortui large ribosomal unit. Pending the implementation of a dedicated web server, the code accompanying this article, written in JAVA, is available upon request from the contact author
Antiferromagnetic spintronics
Antiferromagnetic materials are magnetic inside, however, the direction of
their ordered microscopic moments alternates between individual atomic sites.
The resulting zero net magnetic moment makes magnetism in antiferromagnets
invisible on the outside. It also implies that if information was stored in
antiferromagnetic moments it would be insensitive to disturbing external
magnetic fields, and the antiferromagnetic element would not affect
magnetically its neighbors no matter how densely the elements were arranged in
a device. The intrinsic high frequencies of antiferromagnetic dynamics
represent another property that makes antiferromagnets distinct from
ferromagnets. The outstanding question is how to efficiently manipulate and
detect the magnetic state of an antiferromagnet. In this article we give an
overview of recent works addressing this question. We also review studies
looking at merits of antiferromagnetic spintronics from a more general
perspective of spin-ransport, magnetization dynamics, and materials research,
and give a brief outlook of future research and applications of
antiferromagnetic spintronics.Comment: 13 pages, 7 figure
Room-temperature antiferromagnetic memory resistor
The bistability of ordered spin states in ferromagnets (FMs) provides the
magnetic memory functionality. Traditionally, the macroscopic moment of ordered
spins in FMs is utilized to write information on magnetic media by a weak
external magnetic field, and the FM stray field is used for reading. However,
the latest generation of magnetic random access memories demonstrates a new
efficient approach in which magnetic fields are replaced by electrical means
for reading and writing. This concept may eventually leave the sensitivity of
FMs to magnetic fields as a mere weakness for retention and the FM stray fields
as a mere obstacle for high-density memory integration. In this paper we report
a room-temperature bistable antiferromagnetic (AFM) memory which produces
negligible stray fields and is inert in strong magnetic fields. We use a
resistor made of an FeRh AFM whose transition to a FM order 100 degrees above
room-temperature, allows us to magnetically set different collective directions
of Fe moments. Upon cooling to room-temperature, the AFM order sets in with the
direction the AFM moments pre-determined by the field and moment direction in
the high temperature FM state. For electrical reading, we use an
antiferromagnetic analogue of the anisotropic magnetoresistance (AMR). We
report microscopic theory modeling which confirms that this archetypical
spintronic effect discovered more than 150 years ago in FMs, can be equally
present in AFMs. Our work demonstrates the feasibility to realize
room-temperature spintronic memories with AFMs which greatly expands the
magnetic materials base for these devices and offers properties which are
unparalleled in FMs
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