Reduction of ceramide de novo synthesis in solid tissues changes sphingolipid levels in rat plasma, erythrocytes and platelets

PURPOSE

De novo sphingolipid synthesis does not occur in plasma, erythrocytes and platelets. The purpose of the study was to examine the effect of inhibition of sphingolipid synthesis in solid tissues on the level of the following bioactive sphingolipids: sphinganine, ceramide, sphingosine and sphingosine 1-phosphate in plasma, erythrocytes and platelets.

MATERIAL/METHODS

The experiments were carried out on male Wistar rats. Myriocin was used to inhibit serine palmitoyltransferase activity (the enzyme catalyzes the first step of ceramide de novo synthesis) and nicotinic acid was used to reduce the concentration of plasma free fatty acids (a substrate for the de novo ceramide synthesis). The sphingolipids were quantified by means of liquid chromatography/mass spectrometry.

RESULTS

Myriocin reduced the level of each compound in plasma. It reduced the level of sphinganine, sphingosine-1-phosphate and total ceramide and elevated the level of sphingosine in erythrocytes. In platelets, myriocin reduced the total level of ceramide. Nicotinic acid reduced the plasma level of sphinganine, sphingosine and total ceramide. It increased the level of sphingosine-1-phosphate in erythrocytes. In platelets, nicotinioc acid increased the level of sphinganine and sphingosine and reduced the level of sphingosine-1-phosphate and total ceramide.

CONCLUSIONS

Inhibition of serine palmitoyltransferase activity in solid tissues and reduction in plasma free fatty acids concentration affects sphingolipid level in plasma, erythrocytes and platelets. The changes in erythrocytes and platelets depend both on the cell type and the sphingolipid studied and only partially follow the changes in the plasma.

Adiabatic fast passage application in solid state NMR study of cross relaxation and molecular dynamics in heteronuclear systems

The paper presents the benefits of using fast adiabatic passage for the study of molecular dynamics in the solid state heteronuclear systems in the laboratory frame. A homemade pulse spectrometer operating at the frequency of 30.2MHz and 28.411MHz for protons and fluorines, respectively, has been enhanced with microcontroller direct digital synthesizer DDS controller [1-4]. This work briefly describes how to construct a low-cost and easy-to-assemble adiabatic extension set for homemade and commercial spectrometers based on recently very popular Arduino shields. The described set was designed for fast adiabatic generation. Timing and synchronization problems are discussed. The cross-relaxation experiments with different initial states of the two spin systems have been performed. Contrary to our previous work [5] where the steady-state NOE experiments were conducted now proton spins (1)H are polarized in the magnetic field B0 while fluorine spins (19)F are perturbed by selective saturation for a short time and then the system is allowed to evolve for a period in the absence of a saturating field. The adiabatic passage application leads to a reversal of magnetization of fluorine spins and increases the amplitude of the signal.

Training Does Not Alter Muscle Ceramide and Diacylglycerol in Offsprings of Type 2 Diabetic Patients Despite Improved Insulin Sensitivity

Ceramide and diacylglycerol (DAG) may be involved in the early phase of insulin resistance but data are inconsistent in man. We evaluated if an increase in insulin sensitivity after endurance training was accompanied by changes in these lipids in skeletal muscle. Nineteen first-degree type 2 diabetes Offsprings (Offsprings) (age: 33.1 ± 1.4 yrs; BMI: 26.4 ± 0.4 kg/m²) and sixteen matched Controls (age: 31.3 ± 1.5 yrs; BMI: 25.3 ± 0.7 kg/m²) performed 10 weeks of endurance training three times a week at 70% of VO₂max on a bicycle ergometer. Before and after the intervention a hyperinsulinemic-euglycemic clamp and VO₂max test were performed and muscle biopsies obtained. Insulin sensitivity was significantly lower in Offsprings compared to control subjects (p < 0.01) but improved in both groups after 10 weeks of endurance training (Off: 17 ± 6%; Con: 12 ± 9%, p < 0.01). The content of muscle ceramide, DAG, and their subspecies were similar between groups and did not change in response to the endurance training except for an overall reduction in C22:0-Cer (p < 0.05). Finally, the intervention induced an increase in AKT protein expression (Off: 27 ± 11%; Con: 20 ± 24%, p < 0.05). This study showed no relation between insulin sensitivity and ceramide or DAG content suggesting that ceramide and DAG are not major players in the early phase of insulin resistance in human muscle.

Myocardial lipid profiling during time course of high fat diet and its relationship to the expression of fatty acid transporters

BACKGROUND/AIMS

It is well documented that increased fatty acids (FA) supply causes lipid accumulation and insulin resistance in skeletal muscles. Whether the same mechanism is present in the heart is still unclear. Therefore, the goal of our study was to determine the content of specific myocardial lipid fractions during feeding rats a high fat diet (HFD) for 5 weeks. Moreover, the relation between changes in myocardial lipid content, whole body insulin resistance and the expression of fatty acid transporters in each week of HFD was established.

METHODS

Gas liquid chromatography and high performance liquid chromatography were used to determine the content of lipid fractions in the left ventricle. Expression of selected proteins was estimated by Western blot technique. All measurements were made after each week of HFD.

RESULTS

As expected, lipid profile in myocardium was altered by HFD in different weeks of the study with the most intense changes in triacylglycerols, long chain fatty acid-CoA and ceramide. Furthermore, there was a significant elevation of plasmalemmal (the 4th and the 5th week) and mitochondrial expression (from the 3rd to the 5th week) of fatty acid translocase.

CONCLUSION

High fat diet affects myocardial lipid profile in each week of its duration and causes alternations in FA metabolism in cardiomyocytes.

Sources, metabolism, and regulation of circulating sphingosine-1-phosphate

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that acts either as an intracellular messenger or as a ligand for its membrane receptors. S1P is a normal constituent of blood, where it is found both in plasma and blood cells. Compared with other cell types, sphingolipid metabolism in erythrocytes and platelets has unique features that allow the erythrocytes and platelets to accumulate S1P. In plasma, S1P is bound mainly to HDLs and albumin. Of note, metabolism and biological activity of S1P is to a large extent affected by the type of its carrier. Plasma S1P is characterized by a short half-life, indicating rapid clearance by degradative enzymes and the presence of high-capacity sources involved in maintaining its high concentration. These sources include blood cells, vascular endothelium, and hepatocytes. However, the extent to which each of these contributes to the plasma pool of S1P is a matter of debate. Circulating S1P plays a significant physiological role. It was found to be the key regulator of lymphocyte trafficking, endothelial barrier function, and vascular tone. The purpose of this review is to summarize the present state of knowledge on the metabolism, transport, and origin of plasma S1P, and to discuss the mechanisms regulating its homeostasis in blood.

Effect of atrial pacing on the level of bioactive sphingolipids in the heart ventricles of the rat

Bioactive sphingolipids play important role in regulation of the function of the cardiomyocytes. There are no data available on metabolism of the sphingolipids in the heart under increased work-load produced by tachycardia. The aim of the present study was to examine effect of tachycardia on the level of the principal bioactive sphingolipids in the left and right ventricles. The experiments were carried out on male Wistar rats. After anesthesia, two electrodes were administered into the right common jugular vein so that their tips were placed at the vein's aperture. The resting heart rate was 355 ± 24/min and the rate of stimulation was 600/min. EKG was continuously monitored. The stimulation time was 30 and 60 min. Thereafter, blood from the abdominal aorta and samples of the left and right ventricle were taken. The following bioactive sphingolipids were quantified by means of high performance liquid chromatography: sphinganine, ceramide, sphingosine, sphingosine-1-phosphate and sphinganine-1-phosphate. In the left ventricle, 30 and 60 min tachycardia elevated the level of sphingosine, reduced the level of sphingosine-1-phosphate and sphinganine-1-phosphate. The level of ceramide was reduced only after 60 min. In the right ventricle, 60 min pacing resulted in elevation in the level of sphingosine and sphinganine and reduction in the level of other compounds studied. It is concluded that tachycardia induces changes in metabolism of bioactive sphingolipids in each ventricle. The changes may affect cardiomyocyte functions. Also, differences in sphingolipid metabolism between both ventricles are reported.

Positive effects of voluntary running on metabolic syndrome-related disorders in non-obese hereditary hypertriacylglycerolemic rats

While metabolic syndrome is often associated with obesity, 25% of humans suffering from it are not obese and the effect of physical activity remains unclear in such cases. Therefore, we used hereditary hypertriaclyglycerolemic (HHTg) rats as a unique model for studying the effect of spontaneous physical activity [voluntary running (VR)] on metabolic syndrome-related disorders, such as dyslipidemia, in non-obese subjects. Adult HHTg males were fed standard (CD) or high-sucrose (HSD) diets ad libitum for four weeks. Within both dietary groups, some of the rats had free access to a running wheel (CD+VR, HSD+VR), whereas the controls (CD, HSD) had no possibility of extra physical activity. At the end of the four weeks, we measured the effects of VR on various metabolic syndrome-associated parameters: (i) biochemical parameters, (ii) the content and composition of triacylglycerols (TAG), diacylglycerols (DAG), ceramides and membrane phospholipids, and (iii) substrate utilization in brown adipose tissue. In both dietary groups, VR led to various positive effects: reduced epididymal and perirenal fat depots; increased epididymal adipose tissue lipolysis; decreased amounts of serum TAG, non-esterified fatty acids and insulin; a higher insulin sensitivity index. While tissue ceramide content was not affected, decreased TAG accumulation resulted in reduced and modified liver, heart and skeletal muscle DAG. VR also had a beneficial effect on muscle membrane phospholipid composition. In addition, compared with the CD group, the CD+VR rats exhibited increased fatty acid oxidation and protein content in brown adipose tissue. Our results confirm that physical activity in a non-obese model of severe dyslipidemia has many beneficial effects and can even counteract the negative effects of sucrose consumption. Furthermore, they suggest that the mechanism by which these effects are modulated involves a combination of several positive changes in lipid metabolism.

LXR Agonist T0901317-Induced Hyperlipidemia Does Not Lead to Lipid Accumulation in the Rat Heart

Background/Aims: Liver X receptors (LXRα and LXRβ) are ligand-activated transcription factors that regulate expression of genes involved in lipid and cholesterol metabolism. LXR expression has been identified in human and rodent cardiac tissue, however, its role in this tissue remains unclear. The aim of this study was to investigate effects of in vivo LXR activation on lipid metabolism in the rat myocardium under the conditions of low and high lipid intake. Methods: The experiments were performed on male Wistar rats fed for 5 weeks on either low fat diet (LFD) or high fat diet (HFD). Next, the animals were randomly divided into two groups receiving either LXR agonist - T0901317 (10mg/kg/d) or vehicle for the last week of the experiment. After anesthesia samples of the left ventricle and blood were taken. Results: It was found that LXRβ is the dominant isoform in the rat myocardium and the expression of both LXR isoforms did not change after administration of T0901317. Agonist treatment induced hyperlipidemia in low fat fed rats and this effect was amplified in high fat fed rats. LXR agonist elevated content of myocardial triacylglycerols in animals fed on LFD and content of phospholipids in animals fed on HFD. Levels of the remaining examined lipid classes (nonesterified fatty acids, diacylglycerol, free cholesterol, cholesterol esters, ceramide) was decreased or unchaged after LXR activation. Conclusion: We conclude that administration of T0901317 does not lead to severe myocardial lipid accumulation in rats despite of its high plasma availability.

New evidence for the role of ceramide in the development of hepatic insulin resistance

Aim

There are few and contradictory data on the role of excessive accumulation of intracellular sphingolipids, particularly ceramides, in the development of hepatic insulin resistance. In our study we assessed accumulated sphingolipid fractions and clarify the mechanisms of hepatic insulin resistance development as well as involvement of fatty acid and ceramide transporters in this process.

Methods

In culture of primary rat hepatocytes, exposed to high concentration of palmitic acid (0.75mM) during short and prolonged incubation, high performance liquid chromatography was used to assess intra- and extracellular sphingolipid fractions content. Degree of palmitate-induced insulin resistance was estimated by measuring changes in phosphorylation of insulin pathway proteins by western blotting as well as changes in expression of different type of transporters.

Results

In our study short and prolonged exposure of primary hepatocytes to palmitic acid resulted in increased intracellular accumulation of ceramide which inhibited insulin signaling pathway. We observed a significant increase in the expression of fatty-acid transport protein (FATP2) and ceramide transfer protein (CERT) what is consistent with enhanced intracellular ceramide content. The content of extracellular ceramide was increased nearly threefold after short and twofold after long incubation period. Expression of microsomal triglyceride transfer protein (MTP) and ATP-binding cassette transporter (ABCA1) was increased significantly mainly after short palmitate incubation.

Conclusion

Our data showed that increase in intarcellular ceramide content contributes to the development of hepatic insulin resistance. We suggest pivotal role of transporters in facilitating fatty acid influx (FATP2), accumulation of ceramides (CERT) and export to the media (MTP and ABCA1).

Exercise increases sphingoid base-1-phosphate levels in human blood and skeletal muscle in a time- and intensity-dependent manner

Purpose

Sphingosine-1-phosphate (S1P) regulates cardiovascular function and plays an important role in muscle biology. We have previously reported that cycling exercise increased plasma S1P. Here, we investigated the effect of exercise duration and intensity on plasma and skeletal muscle S1P levels.

Methods

In the first experiment, 13 male athletes performed a 60-min exercise at 65 % of VO_2max and a graded exercise until exhaustion on a rowing ergometer. Samples of the venous blood were taken, and plasma, erythrocytes and platelets were isolated. In the second experiment, ten male moderately active subjects performed three consecutive periods of one-leg knee extension exercise (at 25, 55 and 85 % of the maximal workload). Muscle biopsies and blood samples from the radial artery and femoral veins were taken.

Results

Under basal conditions, S1P was released from the leg, as its concentration was lower in the arterial than in the venous plasma (p < 0.01). Exercise until exhaustion increased plasma S1P and sphinganine-1-phosphate (SA1P) concentration (p < 0.05), whereas moderate-intensity exercise elevated only SA1P (p < 0.001). Although knee extension increased muscle S1P content (p < 0.05), it was not released but taken up across the leg during exercise. However, sphingosine was released from both working and resting leg at the highest workload (p < 0.05).

Conclusions

Plasma S1P concentration is elevated only by high-intensity exercise which results, at least in part, from increased availability of sphingosine released by skeletal muscle. In addition, exercise markedly affects S1P dynamics across the leg. We speculate that S1P may play an important role in adaptation of skeletal muscle to exercise.

Electronic supplementary material

The online version of this article (doi:10.1007/s00421-014-3080-x) contains supplementary material, which is available to authorized users.

Two-dimensional EPR imaging with the rapid scan and rotated magnetic field gradient

A new method for fast 2D Electron Paramagnetic Resonance Imaging (EPRI) is presented. To reduce the time of projections acquisition we propose to combine rapid scan of Zeeman magnetic field using high frequency sinusoidal modulation with simultaneously applied magnetic field gradient, whose orientation is changed at low frequency. The correctness of the method is confirmed by studies carried out on a phantom consisting of two LiPc samples. The images from the acquired data are reconstructed using iterative algorithms. The proposed method allows to reduce the image acquisition time up to 10 ms for 2D EPRI, and to detect the sinogram with infinitesimal angular step between projections.

Two-dimensional spectral-spatial EPR imaging with the rapid scan and modulated magnetic field gradient

A new method for fast spectral-spatial electron paramagnetic resonance imaging (EPRI) is presented. To reduce the time of projections acquisition we propose to combine rapid scan of Zeeman magnetic field using high frequency sinusoidal modulation with simultaneously applied magnetic field gradients, whose amplitude is modulated at low frequency. The correctness of the method is confirmed by studies carried out on a phantom consisting of two LiPc samples. The spectral-spatial images from the acquired data are reconstructed using iterative algorithms. The proposed method allows to acquire the spectral-spatial image with 800 projections at 200ms.

Change in blood gelsolin concentration in response to physical exercise

Plasma gelsolin (pGSN) produced by muscle is an abundant protein of extracellular fluids capable of severing actin filaments and eliminating actin from the circulation. Additionally, pGSN modulates the cellular effects of some bioactive lipids. In this study we test the hypothesis that hormonal and metabolic adaptations to exercise are associated with changes in gelsolin concentration in blood. Plasma samples were collected from twenty healthy males recruited from untrained (UT, n=10) and endurance trained (ET, n=10) groups that performed 30-60 minutes of exercise on a cycloergometer at a workload corresponding to 70% of VO2max. Gelsolin concentration was determined by quantitative Western blot analysis with an anti-human gelsolin antibody. The gelsolin concentration in UT and ET subjects before starting exercise ranged from 104 to 330 and 163 to 337 µg · ml(-1) respectively. After 30 minutes of exercise we observed a significant decrease of plasma gelsolin in the UT group (p<0.05) while the gelsolin concentration in the ET group rose on average from 244 to 271 µg · ml(-1). However, this increase did not reach statistical significance. Endurance training might increase the ability of muscle tissue to express plasma gelsolin as part of an adaptive mechanism.

Effects of inhibition of serine palmitoyltransferase (SPT) and sphingosine kinase 1 (SphK1) on palmitate induced insulin resistance in L6 myotubes

Background

The objective of this study was to examine the effects of short (2 h) and prolonged (18 h) inhibition of serine palmitoyltransferase (SPT) and sphingosine kinase 1 (SphK1) on palmitate (PA) induced insulin resistance in L6 myotubes.

Methods

L6 myotubes were treated simultaneously with either PA and myriocin (SPT inhibitor) or PA and Ski II (SphK1inhibitor) for different time periods (2 h and 18 h). Insulin stimulated glucose uptake was measured using radioactive isotope. Expression of insulin signaling proteins was determined using Western blot analyses. Intracellular sphingolipids content [sphinganine (SFA), ceramide (CER), sphingosine (SFO), sphingosine-1-phosphate (S1P)] were estimated by HPLC.

Results

Our results revealed that both short and prolonged time of inhibition of SPT by myriocin was sufficient to prevent ceramide accumulation and simultaneously reverse palmitate induced inhibition of insulin-stimulated glucose transport. In contrast, prolonged inhibition of SphK1 intensified the effect of PA on insulin-stimulated glucose uptake and attenuated further the activity of insulin signaling proteins (pGSK3β/GSK3β ratio) in L6 myotubes. These effects were related to the accumulation of sphingosine in palmitate treated myotubes.

Conclusion

Myriocin is more effective in restoration of palmitate induced insulin resistance in L6 myocytes, despite of the time of SPT inhibition, comparing to SKII (a specific SphK1 inhibitor). Observed changes in insulin signaling proteins were related to the content of specific sphingolipids, namely to the reduction of ceramide. Interestingly, inactivation of SphK1 augmented the effect of PA induced insulin resistance in L6 myotubes, which was associated with further inhibition of insulin stimulated PKB and GSK3β phosphorylation, glucose uptake and the accumulation of sphingosine.

Mitochondrial substrate availability and its role in lipid-induced insulin resistance and proinflammatory signaling in skeletal muscle

The relationship between glucose and lipid metabolism has been of significant interest in understanding the pathogenesis of obesity-induced insulin resistance. To gain insight into this metabolic paradigm, we explored the potential interplay between cellular glucose flux and lipid-induced metabolic dysfunction within skeletal muscle. Here, we show that palmitate (PA)-induced insulin resistance and proinflammation in muscle cells, which is associated with reduced mitochondrial integrity and oxidative capacity, can be attenuated under conditions of glucose withdrawal or glycolytic inhibition using 2-deoxyglucose (2DG). Importantly, these glucopenic-driven improvements coincide with the preservation of mitochondrial function and are dependent on PA oxidation, which becomes markedly enhanced in the absence of glucose. Intriguingly, despite its ability to upregulate mitochondrial PA oxidation, glucose withdrawal did not attenuate PA-induced increases in total intramyocellular diacylglycerol and ceramide. Furthermore, consistent with our findings in cultured muscle cells, we also report enhanced insulin sensitivity and reduced proinflammatory tone in soleus muscle from obese Zucker rats fed a 2DG-supplemented diet. Notably, this improved metabolic status after 2DG dietary intervention is associated with markedly reduced plasma free fatty acids. Collectively, our data highlight the key role that mitochondrial substrate availability plays in lipid-induced metabolic dysregulation both in vitro and in vivo.

Defining the role of DAG, mitochondrial function, and lipid deposition in palmitate-induced proinflammatory signaling and its counter-modulation by palmitoleate

Chronic exposure of skeletal muscle to saturated fatty acids, such as palmitate (C16:0), enhances proinflammatory IKK-NFκB signaling by a mechanism involving the MAP kinase (Raf-MEK-ERK) pathway. Raf activation can be induced by its dissociation from the Raf-kinase inhibitor protein (RKIP) by diacylglycerol (DAG)-sensitive protein kinase C (PKC). However, whether these molecules mediate the proinflammatory action of palmitate, an important precursor for DAG synthesis, is currently unknown. Here, involvement of DAG-sensitive PKCs, RKIP, and the structurally related monounsaturated fatty acid palmitoleate (C16:1) on proinflammatory signaling are investigated. Palmitate, but not palmitoleate, induced phosphorylation/activation of the MEK-ERK-IKK axis and proinflammatory cytokine (IL-6, CINC-1) expression. Palmitate increased intramyocellular DAG and invoked PKC-dependent RKIP(Ser153) phosphorylation, resulting in RKIP-Raf1 dissociation and MEK-ERK signaling. These responses were mimicked by PMA, a DAG mimetic and PKC activator. However, while pharmacological inhibition of PKC suppressed PMA-induced activation of MEK-ERK-IKK signaling, activation by palmitate was upheld, suggesting that DAG-sensitive PKC and RKIP were dispensable for palmitate's proinflammatory action. Strikingly, the proinflammatory effect of palmitate was potently repressed by palmitoleate. This repression was not due to reduced palmitate uptake but linked to increased neutral lipid storage and enhanced cellular oxidative capacity brought about by palmitoleate's ability to restrain palmitate-induced mitochondrial dysfunction.

[Epicardial adipose tissue and its role in cardiac physiology and disease]

Adipose tissue secretes a number of cytokines, referred to as adipokines. Intensive studies conducted over the last two decades showed that adipokines exert broad effects on cardiac metabolism and function. In addition, the available data strongly suggests that these cytokines play an important role in development of cardiovascular diseases. Epicardial adipose tissue (EAT) has special properties that distinguish it from other deposits of visceral fat. Overall, there appears to be a close functional and anatomic relationship between the EAT and the cardiac muscle. They share the same coronary blood supply, and there is no structure separating the adipose tissue from the myocardium or coronary arteries. The role of EAT in osierdziocardiac physiology remains unclear. Its putative functions include buffering coronary arteries against the torsion induced by the arterial pulse wave and cardiac contraction, regulating fatty acid homeostasis in the coronary microcirculation, thermogenesis, and neuroprotection of the cardiac autonomic ganglia and nerves. Obesity (particularly the abdominal phenotype) leads to elevated EAT content, and the available data suggests that high amount of this fat depot is associated with increased risk of ischemic heart disease, cardiac hypertrophy and diastolic dysfunction. The mass of EAT is small compared to other fat deposits in the body. Nevertheless, its close anatomic relationship to the heart suggests that this organ is highly exposed to EAT-derived adipokines which makes this tissue a very promising area of research. In this paper we review the current knowledge on the role of EAT in cardiac physiology and development of heart disease.

Liver X receptor agonist T0901317 enhanced peroxisome proliferator-activated receptor-delta expression and fatty acid oxidation in rat skeletal muscle

Liver X receptors (LXR) have been characterized as key transcriptional regulators of hepatic lipid and carbohydrate metabolism. LXR are expressed also in skeletal muscle, however, their role in this tissue is poorly investigated and the vast majority of available data comes from studies on cultured myotubes. Therefore, we aimed to examine effects of in vivo LXR activation on muscle lipid metabolism. The experiments were performed on male Wistar rats fed on a standard rodent chow. The animals were divided into two groups (n=10) receiving either LXR activator (T0901317, 10 mg/kg/day) or vehicle for one week. Samples of the soleus as well as red and white sections of the gastrocnemius muscle were excised. T0901317 increased muscle expression of peroxisome proliferator-activated receptor-δ and its target genes involved in fatty acid uptake and oxidation. In addition, LXR agonist enhanced palmitate oxidation (by 55%) in isolated soleus muscle. However, palmitate incorporation into triacylglycerol was decreased (by 38%), which was associated with reduced diacylglycerol acyltransferase expression (by 66%). Despite markedly increased plasma lipid concentration upon T0901317 treatment, muscle triacylglycerol level was elevated only in the red section of the gastrocnemius muscle. We conclude that T0901317 enhances muscle fatty acid oxidation, which prevents overt accumulation of intramuscular lipids that could be expected considering T0901317-induced hyperlipidemia.

Analysis of Uniformity of Magnetic Field Generated by the Two-Pair Coil System

In this paper we use a simple analysis based on properties of the axial field generated by symmetrical multipoles to reveal all possible distributions of two coaxial pairs of circular windings, which result in systems featuring zero octupole and 32 pole magnetic moments (six-order systems). Homogeneity of magnetic field of selected systems is analyzed. It has been found that one of the derived systems generates homogenous magnetic field whose volume is comparable to that yielded by the eight-order system. The influence of the current distribution and the windings placement on the field homogeneity is considered. The table, graphs and equations given in the paper facilitate the choice of the most appropriate design for a given problem. The systems presented may find applications in low field electron paramagnetic resonance imaging, some functional f-MRI (nuclear magnetic resonance imaging) and bioelectromagnetic experiments requiring the access to the working space from all directions.

Enhancement of photoluminescence from GaInNAsSb quantum wells upon annealing: improvement of material quality and carrier collection by the quantum well

In this study we apply time resolved photoluminescence and contactless electroreflectance to study the carrier collection efficiency of a GaInNAsSb/GaAs quantum well (QW). We show that the enhancement of photoluminescence from GaInNAsSb quantum wells annealed at different temperatures originates not only from (i) the improvement of the optical quality of the GaInNAsSb material (i.e., removal of point defects, which are the source of nonradiative recombination) but it is also affected by (ii) the improvement of carrier collection by the QW region. The total PL efficiency is the product of these two factors, for which the optimal annealing temperatures are found to be ~700 °C and ~760 °C, respectively, whereas the optimal annealing temperature for the integrated PL intensity is found to be between the two temperatures and equals ~720 °C. We connect the variation of the carrier collection efficiency with the modification of the band bending conditions in the investigated structure due to the Fermi level shift in the GaInNAsSb layer after annealing.

The Instrument Set for Generating Fast Adiabatic Passage

The design and construction of a high-performance, low-cost, and easy to assemble adiabatic extension set for homebuilt and commercial spectrometers is described. Described apparatus set was designed for the fast adiabatic passage generation and is based on direct digital synthesizer DDS. This solution gives generator high signal to noise ratio, phase stability even during frequency change which is only possible in expansive commercial high-end hardware. Critical synchronization and timing issues are considered and solutions are discussed. Different experimental conditions and techniques for the measurements are briefly discussed. The proposed system is very flexible and might be used for the measurement of low-frequency nuclear magnetic resonance.