Atypical behavior of collective modes in two-dimensional Fermi liquids.

Using the Landau kinetic equation to study the non-equilibrium behavior of interacting Fermi systems is one of the crowning achievements of Landau's Fermi liquid theory. While thorough study of transport modes has been done for standard three-dimensional Fermi liquids, an equally in-depth analysis for two dimensional Fermi liquids is lacking. In applying the Landau kinetic equation (LKE) to a two-dimensional Fermi liquid, we obtain unconventional behavior of the zero sound mode c 0. As a function of the usual dimensionless parameter s = ω/q v F, we find two peculiar results: first, for |s| > 1 we see the propagation of an undamped mode for weakly interacting systems. This differs from the three dimensional case where an undamped mode only propagates for repulsive interactions and the mode experiences Landau damping for any arbitrary attractive interaction. Second, we find that regardless of interaction strength, a propagating mode is forbidden for |s| < 1. This is profoundly different from the three-dimensional case where a mode can propagate, albeit damped. In addition, we present a revised Pomeranchuk instability condition for a two-dimensional Fermi liquid as well as equations of motion for the fluid that follow directly from the LKE. In two dimensions, we find a constant minimum for all Landau parameters for ℓ ⩾ 1 which differs from the three dimensional case. Finally we discuss the effect of a Coulomb interaction on the system resulting in the plasmon frequency ω p exhibiting a crossover to the zero sound mode.

The role of citizen science in addressing grand challenges in food and agriculture research.

The power of citizen science to contribute to both science and society is gaining increased recognition, particularly in physics and biology. Although there is a long history of public engagement in agriculture and food science, the term 'citizen science' has rarely been applied to these efforts. Similarly, in the emerging field of citizen science, most new citizen science projects do not focus on food or agriculture. Here, we convened thought leaders from a broad range of fields related to citizen science, agriculture, and food science to highlight key opportunities for bridging these overlapping yet disconnected communities/fields and identify ways to leverage their respective strengths. Specifically, we show that (i) citizen science projects are addressing many grand challenges facing our food systems, as outlined by the United States National Institute of Food and Agriculture, as well as broader Sustainable Development Goals set by the United Nations Development Programme, (ii) there exist emerging opportunities and unique challenges for citizen science in agriculture/food research, and (iii) the greatest opportunities for the development of citizen science projects in agriculture and food science will be gained by using the existing infrastructure and tools of Extension programmes and through the engagement of urban communities. Further, we argue there is no better time to foster greater collaboration between these fields given the trend of shrinking Extension programmes, the increasing need to apply innovative solutions to address rising demands on agricultural systems, and the exponential growth of the field of citizen science.

Consequences of the inherent density dependence in one dimensional Dirac materials.

Dirac materials are systems in which the dispersion is linear in the vicinity of the Dirac points. As a consequence of this linear dispersion, the Fermi velocity is independent of density and these systems exhibit unusual behavior and possess unique physical properties that are of considerable interest. In this work we study the ground state behavior of 1D Dirac materials in two ways. First, using the Virial theorem, we find agreement with a previous result in regards to the total average ground state energy. Namely, that the total average ground state energy, regardless of dimensionality, is found to be [Formula: see text] where r s is a dimensionless constant that's a measure of density and [Formula: see text] is a constant independent of r s . As a consequence, thermodynamic results as well as the characteristic exponents of 1D Fermi systems are density independent. Second, using conventional techniques, i.e. Tomanaga-Luttinger theory, we find several unique properties that are a direct consequence of the dispersion. Specifically, the collective modes of the system exhibit electron density independence predicted from the Virial theorem. Finally, possible experimental realization of our predictions of density independent exponents are briefly discussed.

Superconductivity near itinerant ferromagnetic quantum criticality.

Superconductivity mediated by spin fluctuations in weak and nearly ferromagnetic metals is studied close to the zero-temperature magnetic transition. We solve analytically the Eliashberg equations for p-wave pairing and obtain the quasiparticle self-energy and the superconducting transition temperature T(c) as a function of the distance to the quantum critical point (QCP). We show that the reduction of quasiparticle coherence and lifetime due to scattering by quasistatic spin fluctuations is the dominant pair-breaking process, which leads to a rapid suppression of T(c) to a nonzero value near the QCP. We point out the differences and similarities of the problem to that of paramagnetic impurities in superconductors.

Angiotensin II in cardiac pressure-overload hypertrophy in fetal sheep.

We previously demonstrated in fetal sheep that blockade of ANG II type 1 (AT(1)) receptors did not attenuate an increase in right ventricle (RV) mass resulting from partial occlusion of the pulmonary artery (PA). We have now determined the effects of AT(2)-receptor blockade (PD-123319, 10 mg. kg(-1). day(-1) continuous iv) on the response of the fetal RV to PA banding for 7 days. Four groups of fetuses (each n = 7) were studied beginning at 126 +/- 1 days gestation (term 145 days). RV weight-to-body weight ratio (RV wt/body wt) increased (P < 0.05) in PA-banded (6.00 +/- 0.09 g/kg) and PA-banded + PD-123319 (6.19 +/- 0.27 g/kg) compared with control (5.17 +/- 0.17 g/kg) and PD-123319-infused (5.27 +/- 0.35 g/kg) fetuses (means +/- SE). Blood pressure and heart rate were similar in all groups. PD-123319 produced a decrease (P < 0.05) in AT(1) but not AT(2) mRNA levels in both fetal ventricles. To examine the effect of ANG II on fetal heart growth, twin fetal sheep were infused with either ANG II (twin received vehicle) or phenylephrine (Phe) (twin received vehicle) continuously for 7 days. Mean arterial blood pressure was 20-25 mmHg higher in ANG II and Phe fetuses compared with controls. The rate-pressure product was similar in ANG II and Phe fetuses and 40-50% greater than controls. Phe resulted in no change in RV wt/body wt or left ventricle-to-body weight ratio (LV wt/body wt) compared with controls. In contrast, ANG II produced a selective increase (27 +/- 5%, P < 0.05) in LV wt/body wt; no effect was seen on the RV. ANG II produced a decrease (P < 0.05) in LV but not RV AT(1) mRNA levels compared with controls; no effect was seen with Phe. The data demonstrate that in the ovine fetus, AT(2) receptors do not contribute to the maintenance of blood pressure or the development of pressure-overload RV hypertrophy. Elevated ANG II levels produce a selective increase in LV mass in the fetal sheep that is, in part, independent of increased systolic load.

Coexistence of superconductivity and ferromagnetism in ferromagnetic metals.

We address the question of coexistence of superconductivity and ferromagnetism. Using a field theoretical approach we study a one-fermion effective model of a ferromagnetic superconductor in which the quasiparticles responsible for the ferromagnetism form the Cooper pairs as well. For the first time we solve self-consistently the mean-field equations for the superconducting gap and the spontaneous magnetization. We discuss the physical features which are different in this model and the standard BCS model and consider their experimental consequences.

Glucocorticoid modulation of cardiovascular and autonomic function in preterm lambs: role of ANG II.

The mechanisms by which antenatal glucocorticoids facilitate postnatal circulatory function in preterm infants are uncertain but may be related to augmented angiotensinergic functions. To test the hypothesis that the effects of glucocorticoids on postnatal cardiovascular and sympathetic activity are mediated via the renin-angiotensin system, we studied the effects of AT(1) receptor blockade on postnatal changes in heart rate (HR), mean arterial blood pressure (MABP), renal sympathetic nerve activity (RSNA), and baroreflex control of HR in prematurely delivered lambs. After maternal administration of betamethasone (12 mg im 48 and 24 h before delivery), chronically instrumented preterm lambs (118- to 123-day gestation, term 145 days) were studied before and after delivery by cesarean section; fetuses received either the AT(1) receptor antagonist losartan (10 mg iv, n = 6) or saline (n = 6) 1 h before delivery. A third group of animals (n = 6) received losartan without prior exposure to betamethasone. Compared with fetal values, betamethasone-treated animals demonstrated significant increases (P < 0.05) in MABP (47 +/- 2 to 58 +/- 2 mmHg) and RSNA (181 +/- 80% of fetal value) 1 h after delivery. Betamethasone + losartan-treated lambs also displayed increases in MABP (48 +/- 1 to 55 +/- 3 mmHg) and RSNA (198 +/- 96% of fetal value) 60 min after birth, similar to betamethasone alone lambs. Losartan alone treated animals had no postnatal increase in either MABP or RSNA, responses similar to those seen in nontreated sheep delivered at the same gestational age. The sensitivity of baroreflex-mediated changes in HR in response to increases in MABP was less in both groups of betamethasone-treated animals; no effect was seen with losartan. These results suggest the postnatal increases in MABP and RSNA seen with antenatal glucocorticoid treatment are not mediated by stimulation of peripherally accessible AT(1) receptors. We speculate that augmented cardiovascular function in glucocorticoid-treated premature lambs is dependent, in part, on a generalized sympathoexcitatory response and that this effect of glucocorticoids is mediated by central mechanisms.

Ontogeny and regulation of cardiac angiotensin types 1 and 2 receptors during fetal life in sheep.

Previous studies have shown that the expression of cardiac angiotensin II (ANG II) type 1 (AT1) and type 2 (AT2) receptors are developmentally regulated, although factors modulating these receptors have not been well investigated. The present study was designed 1) to characterize the ontogeny of cardiac AT1 and AT2 gene expression during the last third trimester of gestation in fetal sheep and newborn lambs, 2) to determine the influence of ANG II on modulating cardiac AT1 and AT2 gene expression during fetal life, and 3) to investigate the role of AT1 receptor activity on the regulation of AT1 and AT2 mRNA levels during fetal cardiac development. Using sheep AT1 and AT2 cDNA probes, we demonstrated that cardiac AT1 gene expression is relatively unchanged during fetal (90-135 d of gestation, term 145 d) and newborn life. In contrast, cardiac AT2 mRNA expression was high during fetal development and decreased rapidly after birth. Continuous i.v. infusion of ANG II (9.5 nM/h) for 24 h, which raised ANG II levels from 84+/-9 to 210+/-21 pg/mL had no effect on the expression of cardiac AT1 or AT2 mRNA, but increased adrenal and decreased liver AT1 mRNA levels. Administration of the AT1 receptor antagonist losartan (1.2 mg kg(-1) h(-1)) significantly decreased arterial blood pressure in fetuses at 110- and 135-d, but not 95-d gestation. Except for increased AT1 receptor gene expression in the right atrium at 95- and 135-d gestation, and left ventricle at 110-d gestation, cardiac AT1 and AT2 mRNA levels were unaltered by AT1 receptor blockade. In summary, this study demonstrates that cardiac AT2 but not AT1 receptor gene expression is regulated by the transition from fetal to newborn life. Neither ANG II nor blockade of AT1 receptors significantly alter the expression of AT1 or AT2 mRNA in the fetal heart. Endogenous ANG II also appears to significantly contribute to the maintenance of blood pressure homeostasis during the final third of gestation in fetal lambs.

Development of baroreflex influences on heart rate variability in preterm infants.

To investigate developmental changes in autonomic cardiovascular reflexes in preterm infants, we used autoregressive power spectral analysis to analyze the effect of upright tilting on heart rate variability in preterm infants. Twenty-eight infants were studied in a longitudinal fashion beginning at 28-32 weeks postconceptional age (postnatal age 1-5 weeks). Each week, heart rate variability in the supine position and after 45 degrees head-up tilt was analyzed by spectral analysis. With the initial study of each infant, there was no significant change in heart rate following head-up tilt compared with baseline (-0.5+/-0.9 bpm). However, linear regression analysis revealed that with increasing postnatal age, the change in heart rate in response to tilting became more positive (mean slope of regressions 0.45+/-0.12 bpm/week, P<0.005). The power spectral density of R-R interval variability in the low-(LF; 0.02-0.15 Hz) and high-(HF; 0.15-1.5 Hz) frequency ranges were obtained and the values normalized by dividing each component by the total power. For measurements obtained in the supine position, the LF/HF ratio progressively decreased with increasing postnatal age, indicating a maturational change in sympathovagal balance. We used the difference in the LF/HF ratio between tilt and the recumbent position as a measure of the change in autonomic input to the heart in response to unloading of the arterial baroreceptors. No significant change in these ratios were observed when infants were first studied between 28 and 32 weeks postconceptional age, suggesting that the cardiac baroreflex is poorly developed at this stage of development. However, with postnatal maturation, the LF component of the power spectrum became progressively larger with tilt relative to the basal state, such that the difference between LF/HF(tilt) and LF/HF(base) became progressively more positive (P <0.006). These findings suggest that in premature infants, cardiac baroreceptor reflexes become more functional with postnatal development.

Angiotensin AT1 receptor blockade fails to attenuate pressure-overload cardiac hypertrophy in fetal sheep.

We examined the hypothesis that endogenous angiotensin II and angiotensin type 1 (AT1) receptors participate in the development of fetal right ventricular hypertrophy by studying the effects of AT1 receptor blockade on cardiac growth in fetal sheep subjected to constrictive banding of the pulmonary artery (PA). Seven pairs of twin fetuses were studied beginning at 126 +/- 1 days gestation (term = 145 days). One twin was given losartan (10 mg kg(-1) x day(-1) i.v.) for 7 consecutive days after PA banding, and the other twin served as a saline-treated, PA-banded control. Four additional pairs of twins served as sham-operated controls. Fetal heart rate (HR) and mean arterial blood pressure (MABP) were similar in the two groups of PA-banded animals before treatment and remained unchanged in the PA-banded control group. Losartan resulted in a significant decrease (P < 0.05) in MABP between days 0 and 7, whereas HR was not affected. Total body weight of the losartan-treated animals was significantly less (P < 0.05) than twin PA-banded controls and nonbanded fetuses. Right ventricle weight-to-body weight ratios were similar in saline (2.29 +/- 0.34 g/kg) and losartan-treated (2.11 +/- 0.15 g/kg) PA-banded animals and significantly greater than that in nonbanded fetuses (1.52 +/- 0.07 g/kg). Similar differences were seen in the right ventricle weight-to-left ventricle weight ratios. Right and left ventricle AT1 receptor mRNA and protein expression were also similar among the three groups, as were AT2 receptor mRNA levels. These data suggest that endogenous angiotensin II does not contribute to the development of pressure overload-induced right ventricular hypertrophy during fetal life and that expression of angiotensin receptors is not altered by increased afterload in the ovine fetus.

Effects of functional electrical stimulation-induced lower extremity cycling on bone density of spinal cord-injured patients.

Spinal cord-injured (SCI) patients are at increased risk for fractures secondary to neurogenic osteoporosis. Earlier research claimed physical conditioning resulted in a decreased incidence or reversal of neurogenic osteoporosis. This study evaluated the effects of functional electrical stimulation-induced lower extremity cycling (FESILEC) on the bone densities of SCI patients using dual-energy x/ray absorptiometry (DEXA). The study consisted of 12 healthy male SCI patients, aged 23 to 46 (x +/- SD, 34 +/- 6) yr. The patients were post-traumatic, complete, spastic SCI; time postinjury ranged from 2 to 19 (9.7 +/- 5.1) yr. Patients participated in a three-phase training program. Phase 1 consisted of quadriceps strengthening. Phase 2 consisted of progressive sequential stimulation of quadriceps, hamstrings, and gluteal muscles, achieving a rhythmical pedaling motion on the REGYS I ergometer. Phase 3a consisted of 30-min FESILEC sessions. DEXAs were done at baseline and at completion of Phase 3a and Phase 3b. Bone densities were done of the lumbar spine levels 2-4 (L2-4), bilateral trochanters (T), Ward's triangles (WT) and femoral necks (FN). Baseline bone density indicated no difference between L2-4 of ambulatory males and SCI males. Baseline values obtained for T, WT, and FN were, respectively, 71, 82, and 79% of ambulatory values. Results after completion of the Phase 3a training program indicated no statistically significant difference compared with baseline values. There was, however, a positive trend in the lumbar spine post-Phase 3a (L2-4, P=0.056). Eight patients continued the exercise program, using a combination of upper and lower extremity cycling (Phase 3b) for a longer period of time (25 +/- 9 wk). DEXAs done after Phase 3b indicated no change relative to baseline data or data post-Phase 3a. In conclusion, although FESILEC did not significantly increase bone density in the hip parameters of chronic SCI patients, a positive trend was observed in the lumbar spine. Further research with acute intervention, such as FESILEC during the first few months post-SCI, is warranted to further evaluate a treatment regimen to prevent or reduce neurogenic osteopenia.

Effect of cortisol on gene expression of the renin-angiotensin system in fetal sheep.

Components of the renin-angiotensin system have been found in a variety of tissues during fetal and postnatal life and appear to be developmentally regulated. We postulated that hormonal changes associated with parturition participate in the regulation of renin, angiotensinogen (Ao) and angiotensin type 1 receptor (AT1) gene expression. Cortisol, which increases rapidly in fetal blood before delivery, has been shown to influence the maturation of various systems in the developing fetus. To test the hypothesis that an increase in cortisol regulates fetal renin. Ao, and AT1 mRNA gene expression, we used Northern blot analysis to study the effects of an intraperitoneal infusion of cortisol (3 mg/h, 1 mL/h) for 48 h on the expression of these genes in twin ovine fetuses (n = 10 pairs) at 130-d gestation (term 145 d); one twin in each pair served as a saline-treated control (0.9% NaCl, 1 mL/h). Plasma cortisol levels were significantly higher in cortisol-treated fetuses (113 +/- 23 nmol/dL) than in twin controls (4.6 +/- 0.8 nmol/dL). Cortisol infusion significantly decreased AT1 receptor mRNA levels in kidney and liver by 24 +/- 7% and 27 +/- 8%, respectively, when compared with controls (p < 0.05), whereas in contrast, increased mRNA levels (p < 0.05) in heart right atrium (91 +/- 23%) and ventricle (59 +/- 20%). Renin mRNA levels decreased in renal cortex by 77 +/- 13% (p < 0.05) in cortisol-treated animals compared with controls. Hepatic Ao mRNA levels decreased by 15 +/- 5% in response to cortisol (p < 0.05), whereas no significant effect was seen on renal Ao gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

The conductance of cultured epithelial cell monolayers: oxidants, adenosine triphosphate, and phorbol dibutyrate.

Oxidants are one class of inflammatory molecules that may contribute to an increase in epithelial permeability to water and solutes that commonly occurs during acute inflammation. We and others have observed that oxidants reversibly alter the paracellular conductance of Madin Darby canine kidney epithelial (MDCK) cell monolayers. The mechanism by which oxidants reversibly alter MDCK monolayer conductance is not yet fully understood. Some investigators have suggested that oxidants might alter MDCK monolayer paracellular conductance by depleting adenosine triphosphate (ATP) in the cells. When we exposed MDCK cells to doses of oxidants that increased monolayer paracellular conductance in earlier studies, ATP was depleted within 10 min. However, when ATP was depleted to similar levels with an inhibitor of glycolytic ATP production, 2-deoxy-D-glucose (DOG), monolayer paracellular conductance was not increased. Severe ATP depletion with DOG and the mitochondrial metabolic inhibitor, antimycin A (AA), had very limited, ATP-independent effects on paracellular conductance. As an alternative explanation for the effects of oxidants on MDCK monolayer paracellular conductance, we had reported that oxidants increased production of inositol phosphates and diglycerides in MDCK cells. Synthetic diglyceride and phorbol dibutyrate (PDBU) increased MDCK monolayer conductance to ions and mannitol in earlier studies. When MDCK cell ATP was depleted with DOG (to the level caused by oxidants), the increase in conductance following PDBU was not different from that observed in control cells. More severe ATP depletion, with DOG and AA, prevented the increase in conductance following PDBU.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide blocks the renal vasoconstrictor response to hypertonic saline in the dog.

The role of atrial natriuretic peptide to modulate the renal tubuloglomerular feedback response was examined in the dehydrated anesthetized dog using an infusion of hypertonic sodium chloride to increase renal plasma sodium concentration by 30 mEq/l as the stimulus to activate the tubuloglomerular feedback. Two sequential infusions of hypertonic sodium chloride into the renal artery for 10 min were separated by 90 min, and various interventions were introduced before the second hypertonic saline infusion. In the first group of dogs, the first infusion of hypertonic saline resulted in a significant decrease in renal blood flow from 234 +/- 36 to 199 +/- 31 ml/min, but when atriopeptin III (APIII) was infused into the renal artery at 3 x 10(-10) mol/min, the repeat infusion of hypertonic saline resulted in a significant increase in blood flow from 221 +/- 28 to 269 +/- 35 ml/min that was maintained throughout the 10 min of hypertonic saline. In the second group of dogs only the vehicle for APIII was infused during the second hypertonic saline infusion. In these dogs, renal blood flow decreased significantly the first time from 201 +/- 17 to 170 +/- 16 ml/min, and the second time from 232 +/- 22 to 177 +/- 20 ml/min. In a third group of dogs, the vasodilator sodium nitroprusside, a stimulator of smooth muscle soluble guanylate cyclase, was infused into the renal artery during the second hypertonic saline infusion.(ABSTRACT TRUNCATED AT 250 WORDS)