Tuning Nonlinear Mechanical Mode Coupling in GaAs Nanowires Using Cross-Section Morphology Control.

We investigate the nonlinear mechanical properties of GaAs nanowires with anisotropic cross-section. Fundamental and second order flexural modes are studied using laser interferometry with good agreement found between experiment and theory describing the nonlinear response under mechanical excitation. In particular, we demonstrate that the sign of the nonlinear coupling between orthogonal modes is dependent on the cross-section aspect ratio. The findings are of interest for applications such as amplitude to frequency conversion and vectorial force sensing.

Interplay between spin proximity effect and charge-dependent exciton dynamics in MoSe2/CrBr3 van der Waals heterostructures.

Semiconducting ferromagnet-nonmagnet interfaces in van der Waals heterostructures present a unique opportunity to investigate magnetic proximity interactions dependent upon a multitude of phenomena including valley and layer pseudospins, moiré periodicity, or exceptionally strong Coulomb binding. Here, we report a charge-state dependency of the magnetic proximity effects between MoSe2 and CrBr3 in photoluminescence, whereby the valley polarization of the MoSe2 trion state conforms closely to the local CrBr3 magnetization, while the neutral exciton state remains insensitive to the ferromagnet. We attribute this to spin-dependent interlayer charge transfer occurring on timescales between the exciton and trion radiative lifetimes. Going further, we uncover by both the magneto-optical Kerr effect and photoluminescence a domain-like spatial topography of contrasting valley polarization, which we infer to be labyrinthine or otherwise highly intricate, with features smaller than 400 nm corresponding to our optical resolution. Our findings offer a unique insight into the interplay between short-lived valley excitons and spin-dependent interlayer tunneling, while also highlighting MoSe2 as a promising candidate to optically interface with exotic spin textures in van der Waals structures.

The valley Zeeman effect in inter- and intra-valley trions in monolayer WSe2.

Monolayer transition metal dichalcogenides (TMDs) hold great promise for future information processing applications utilizing a combination of electron spin and valley pseudospin. This unique spin system has led to observation of the valley Zeeman effect in neutral and charged excitonic resonances under applied magnetic fields. However, reported values of the trion valley Zeeman splitting remain highly inconsistent across studies. Here, we utilize high quality hBN encapsulated monolayer WSe2 to enable simultaneous measurement of both intervalley and intravalley trion photoluminescence. We find the valley Zeeman splitting of each trion state to be describable only by a combination of three distinct g-factors, one arising from the exciton-like valley Zeeman effect, the other two, trion specific, g-factors associated with recoil of the excess electron. This complex picture goes significantly beyond the valley Zeeman effect reported for neutral excitons, and eliminates the ambiguity surrounding the magneto-optical response of trions in tungsten based TMD monolayers.

Valley coherent exciton-polaritons in a monolayer semiconductor.

Two-dimensional transition metal dichalcogenides (TMDs) provide a unique possibility to generate and read-out excitonic valley coherence using linearly polarized light, opening the way to valley information transfer between distant systems. However, these excitons have short lifetimes (ps) and efficiently lose their valley coherence via the electron-hole exchange interaction. Here, we show that control of these processes can be gained by embedding a monolayer of WSe2 in an optical microcavity, forming part-light-part-matter exciton-polaritons. We demonstrate optical initialization of valley coherent polariton populations, exhibiting luminescence with a linear polarization degree up to 3 times higher than displayed by bare excitons. We utilize an external magnetic field alongside selective exciton-cavity-mode detuning to control the polariton valley pseudospin vector rotation, which reaches 45° at B = 8 T. This work provides unique insight into the decoherence mechanisms in TMDs and demonstrates the potential for engineering the valley pseudospin dynamics in monolayer semiconductors embedded in photonic structures.

Urinary leukotriene E4 levels increase upon exposure to hypobaric hypoxia.

STUDY OBJECTIVE: To determine whether urinary leukotriene E4 (uLTE4) levels increase upon exposure to high altitude, and also to ascertain the relationship between uLTE4 levels and symptoms of acute mountain sickness (AMS). DESIGN: Prospective, unblinded, single-factor (altitude) experimental study. SETTINGS: US Army research laboratory facilities at sea level ([SL] 50 m), 1,830 m, and 4,300 m. PARTICIPANTS: Eight healthy male subjects ranging in age from 19 to 24 years. MEASUREMENTS: uLTE4 levels and symptoms of AMS were measured at just above SL (50 m), 3 1/2 days after being transported from SL to moderate altitude (MA) (1,830 m), and 1 1/2 days after ascent from 1,830 to 4,300 m (high altitude [HA]). Symptoms of AMS were assessed using standard indexes derived from the Environmental Symptoms Questionnaire weighted toward cerebral (AMS-C) and respiratory (AMS-R) manifestations. Oxygen saturation was measured noninvasively by pulse oximetry at SL and HA. RESULTS: The mean (+/-SEM) uLTE4 levels (pg/mg creatinine) were 67.9 (+/-13.2) at SL; 82.3 (+/-5.5) at MA; and 134.8 (+/-19.4) at HA (p < 0.05 comparing HA with SL and MA). CONCLUSIONS: We conclude that uLTE4 levels increase shortly after exposure to HA even after staging for 4 days at MA. Although this study does not clearly demonstrate a relationship between uLTE4 levels and symptoms of AMS, it supports the hypothesis that leukotrienes may be involved in the pathophysiologic state of AMS.

Altitude acclimatization and blood volume: effects of exogenous erythrocyte volume expansion.

We studied sea-level residents during 13 days of altitude acclimatization to determine 1) altitude acclimatization effects on erythrocyte volume and plasma volume, 2) if exogenous erythrocyte volume expansion alters subsequent erythrocyte volume and plasma volume adaptations, 3) if an increased blood oxygen content alters erythropoietin responses during altitude acclimatization, and 4) mechanisms responsible for plasma loss at altitude. Sixteen healthy men had a series of hematologic measurements made at sea level, on the first and ninth days of altitude (4,300 m) residence, and after returning to sea level. Twenty-four hours before the ascent to altitude, one group received a 700-ml infusion of autologous erythrocytes (42% hematocrit), whereas the other group received only a saline infusion. Erythrocyte infusion increased erythrocyte volume by approximately 10%, whereas saline infusion had no effect; in addition, initially at altitude, blood oxygen content was 8% higher in erythrocyte-infused than in saline-infused subjects. The new findings regarding altitude acclimatization are summarized as follows: 1) erythrocyte volume does not change during the first 13 days and is not affected by prior exogenous expansion, 2) a modest increase in blood oxygen content does not modify erythropoietin responses, 3) plasma losses are related to vascular protein losses, and 4) exogenous erythrocyte volume expansion coincides with transient increases in plasma loss, vascular protein loss, and mean arterial pressure elevation. These findings better define human blood volume responses during altitude acclimatization.

Glycerol-induced hyperhydration: its effects on fluid compartments in the rat.

Glycerol solutions are a safe, effective means to achieve a long-term state of hyperhydration. The effects of glycerol-induced hyperhydration (GIH) on the total body water (TBW), extracellular fluid (ECF), plasma volume (PV), intracellular fluid (ICF), and interstitial fluid (ISF) were investigated in the rat. Ten rats were intragastrically administered either 20 ml/kg of water or 5% glycerol. The TBW, ECF, and PV were determined by 3H2O, 14C-inulin and dye dilution, respectively at 2 h postingestion. Urine volumes and fluid retention were measured throughout the experiment. Fluid retention was increased by 50% with the 5% glycerol solution when compared to water. When the fluid compartment data at 2 h are expressed in terms of percent of body weight, the TBW and ICF of the glycerol-treated rats exceeds that of the water-treated rats, and the values for the ECF, PV, and ISF were similar after the glycerol solution and water regimens. Glycerol solutions appear to have a greater effect in expanding TBW and ICF than equal volumes of water.

Effects of glycerol-induced hyperhydration prior to exercise in the heat on sweating and core temperature.

Hypohydration reduces exercise performance and thermoregulatory capacity in the heat. Hyperhydration prior to exercise may decrease, delay, or eliminate the detrimental effects of hypohydration. The rapid clearance of excess fluid makes hyperhydration of subjects with common beverages difficult. Glycerol, a natural metabolite which is rapidly absorbed, has osmotic action, and is evenly distributed within the body fluid compartments, was tested as a possible hyperhydrating agent. In six subjects, the following fluid regimens at time 0 were randomly administered on three separate days: in trial 1, glycerol (1 g.kg-1 body weight) plus water (21.4 ml.kg-1 body weight); in trial 2, water (21.4 ml.kg-1); and in trial 3, water (3.3 ml.kg-1) was ingested at time 0. The subjects performed moderate exercise (equivalent to 60% VO2max in a comfortable environment) in a hot dry environment. The exercise started at 2.5 h after the fluids were ingested. The urine volume prior to exercise was decreased when glycerol was ingested, thus resulting in glycerol-induced hyperhydration. During the exercise following the glycerol-induced hyperhydration, there was elevated sweat rate and lower rectal temperature during the moderate exercise in the heat. There were no changes in hemoglobin, hematocrit, or serum electrolyte concentrations following glycerol intake. These data support the hypothesis that glycerol-induced hyperhydration reduces the thermal burden of moderate exercise in the heat.

Exercise responses after altitude acclimatization are retained during reintroduction to altitude.

Following 2 to 3 wk of altitude acclimatization, ventilation is increased and heart rate (HR), plasma volume (PV), and lactate accumulation ([La]) are decreased during submaximal exercise. The objective of this study was to determine whether some degree of these exercise responses associated with acclimatization would be retained upon reintroduction to altitude (RA) after 8 d at sea level (SL). Six male lowlanders (X +/- SE; 31 +/- 2 yr, 82.4 +/- 4.6 kg) exercised to exhaustion at the same relative percentages of peak oxygen uptake (VO2peak) at SL, on acute altitude (AA) exposure, after a 16-d chronic altitude (CA) exposure on Pikes Peak (4,300 m), and during a 3- to 4-h RA in a hypobaric chamber (4,300 m; 446 mm Hg) after 8 d at SL. The submaximal exercise to exhaustion time (min) was the same at SL (66.0 +/- 1.6), AA (67.7 +/- 7.3), CA (79.9 +/- 6.2), and RA (67.9 +/- 1.9). At 75% VO2peak: (1) arterial oxygen saturation (SaO2) increased from AA to CA (67.0 +/- 1.5 vs 78.5 +/- 1.8%; P < 0.05) and remained increased at RA (77.0 +/- 2.0%); (2) HR decreased from SL to CA (171 +/- 6 vs 152 +/- 9 beats x min-1; P < 0.05) and remained decreased at RA (157 +/- 5 beats x min-1); (3) calculated PV decreased 6.9 +/- 10.0% at AA, 21.3 +/- 11.1% at CA, and 16.7 +/- 5.4% at RA from SL baseline values, and (4) [La] decreased from AA to CA (5.1 +/- 0.9 vs 1.9 +/- 0.4 mmol x L-1; P < 0.05) and remained decreased at RA (2.6 +/- 0.6 mmol x L-1). Upon RA after 8 d at SL, the acclimatization responses were retained 92 +/- 9% for SaO2, 74 +/- 8% for PV, and 58 +/- 3% for [La] at 75% VO2peak. In conclusion, although submaximal exercise to exhaustion time is not improved upon reintroduction to altitude after 8 d at sea level, retention of beneficial exercise responses associated with altitude acclimatization is likely in individuals whose work, athletic competition, or recreation schedules involve intermittent sojourns to high elevations.

Extraction of benzoylecgonine from urine specimens with Cerex Polycrom Clin II solid-phase extraction columns and the Speedisk Pressure Processor.

Benzoylecgonine (BZE) extraction from urine was explored using Cerex Polycrom Clin II solid-phase extraction (SPE) columns and the Speedisk 48 Pressure Processor as an alternative to the Prep1 automated sample processor and XTRX Type RP/W columns. Linearity for urine standards extracted using the Cerex-Speedisk method ranged from 20 to 3000 ng/mL. The mean recovery at the 100-ng/mL cutoff for three lots of columns was 92%. The mean of the within-run means for three batches, which had coefficients of variations of 1.8% or less, was 101.3 ng/mL at the 100-ng/mL cutoff level. Forty-six specimens known to contain BZE were analyzed by both the Prep1-Type RP/W and Cerex-Speedisk methods. The correlation for specimen BZE concentrations between the two methods gave an r2 of 0.9999 and a slope of 1.03. The Cerex-Speedisk system is an inexpensive alternative to the Prep1-Type RP/W system. It is less costly, requires little maintenance, has a small footprint, is hood compatible, and can process four times the number of specimens in a given time.

A comparison of Roche Kinetic Interaction of Microparticles in Solution (KIMS) assay for cannabinoids and GC-MS analysis for 11-nor-9-carboxy-delta9-tetrahydrocannabinol.

In this study, we investigated the effectiveness of the Roche Kinetic Interaction of Microparticles in Solution (KIMS) screening assay for cannabinoid metabolites. Urine specimens (N = 1689) were collected during elimination of cannabinoids from 25 subjects with a history of marijuana use. Specimens were analyzed concurrently for cannabinoid metabolites by a customized Department of Defense (DOD) cannabinoid KIMS kit (50-ng/mL cutoff) and for 11-nor-9-carboxy-delta9-tetrahydrocannabinol (THC-COOH) by GC-MS (15-ng/mL cutoff). As compared to GC-MS results, the sensitivity, specificity, and efficiency of the KIMS assay were 69.7%, 99.8%, and 88.6%, respectively. Many of the false-negative results had GC-MS concentrations between 15 and 26 ng/mL (N = 151). The cannabinoid screening results for the DOD samples tested by the laboratory during the same 8-month period were also evaluated. The linear regression analyses of GC-MS results in the 15-50 ng/mL range and KIMS data resulted in regression coefficients of 0.689 for the research specimens and 0.546 for DOD specimens. The results suggest that the KIMS cannabinoid screening assay is deficient in detecting positives around the cutoff (15-25 ng/mL THC-COOH). This limitation of the KIMS cannabinoid screening method compromises the identification of true positive specimens, therefore reducing the effectiveness of the assay. The success of the DOD program is dependent on sensitive and specific screening assays; the high prevalence of false-negative cannabinoid results compromises the program's primary objective of drug deterrence.

The effect of altitude pre-acclimatization on acute mountain sickness during reexposure.

BACKGROUND: Acclimatization to high altitude appears to prevent acute mountain sickness (AMS), as evidenced by a decline in AMS symptoms as acclimatization progresses. HYPOTHESIS: We hypothesized that partial retention of acclimatization would attenuate the incidence and/or severity of AMS upon reinduction to altitude. METHODS: To test this hypothesis 6 male lowlanders returned to sea level after the acclimatizing of the 16 d at 4300 m (HA). After 8 d at sea level (PA), they were reexposed to 4300 m in a hypobaric chamber for 30 h (RA). AMS symptom severity was determined by the AMS-cerebral (AMS-C) scores calculated from the daily administration of the Environmental Symptoms Questionnaire during HA and RA. RESULTS: The mean AMS-C scores were reduced from 0.6 on HA day 1 (HA1) to 0.1 during RA (p < 0.05). Four subjects were "sick" (AMS-C > 0.7) during HA1, while only one was "sick" during RA. The % oxyhemoglobin, hemoglobin concentration and hematocrit were higher during RA compared to HA1. CONCLUSIONS: These results suggest that the retention of acclimatization after 8 d at low altitude is sufficient to attenuate AMS upon reinduction to high altitude.

Intraocular pressure and acclimatization to 4300 M altitude.

BACKGROUND: Studies were conducted to determine the effect of altitude exposure on intraocular pressure (IOP) and any relationship with the severity of acute mountain sickness (AMS). HYPOTHESES: a) IOP is decreased during exposure to 4300 m altitude; b) there is a positive correlation between IOP and AMS; and c) there is a correlation between changes in urinary catecholamines and IOP. METHODS: IOP (noncontact tonometry) was measured in 11 resting males during acute simulated altitude (446 mmHg, < 2 h, hypobaric chamber), during altitude acclimatization (15 d at 4300 m), and in 6 of the 11 volunteers during re-exposure in the chamber after 8 d at sea level (Study A). In a second study (Study B) of 12 females, IOP (contact tonometry) and 24-h urinary catecholamines were measured during a 50-h chamber exposure (446 mmHg). AMS severity was assessed using the Environmental Symptoms Questionnaire (ESQ-C). RESULTS: IOP decreased 25% after 2 d at altitude and returned toward sea level values by 15 d (Study A). IOP was reduced 13% after 5 h of exposure followed by return toward sea level values (Study B). Significant correlation was found between the sea level IOP and ESQ-C (Study A); significant correlation was found between the reduction in IOP and the ESQ-C and urinary epinephrine concentrations (Study B). CONCLUSIONS: Altitude exposure resulted in a reduction in IOP that occurred within hours and recovered during acclimatization. This reduction may be related to increases in epinephrine concentration. Measurement of IOP before and during altitude exposure may provide an objective method of assessing an individual's response to hypoxic stress.