Determining Curie temperature of (Ga,Mn)As samples based on electrical transport measurements: low Curie temperature case

In this paper we show that the widely accepted method of the determination of Curie temperature (TC) in (Ga,Mn)As samples, based on the position of the peak in the temperature derivative of the resistivity,completely fails in the case of non-metallic and low-TC unannealed samples. In this case we propose an alternative method, also based on electric transport measurements, which exploits temperature dependence of the second derivative of the resistivity upon magnetic field.Comment: 5 pages, 3 figure

Consistency among Office, Home, and Ambulatory Blood Pressure Values in Women with Chronic Hypertension and History of Eclampsia or Preeclampsia

Adequate control of blood pressure (BP) is essential to prevent complications in pregnant women with a history of eclampsia or pre-eclampsia. However, the importance of office (OBPM), home (HBPM), and ambulatory (ABPM) BP measurements for proper control and prognosis in high-risk pregnancy is unknown. The present study aimed to compare BP values obtained during these three different BP measurements in women with a history of eclampsia or pre-eclampsia. This study included 79 pregnant women with chronic hypertension and a documented history of eclampsia or pre-eclampsia in previous pregnancy/pregnancies. Every fifth week of the study, all participants underwent ABPM, HBPM and OBPM. BP values from the 10th, 25th, and 37th weeks of pregnancy were evaluated. Therapy was intended to meet the ABPM treatment goal of <130/80 mmHg. Day, night, and 24 h ABPM systolic BP values were lower than HBPM and OBPM values at each study visit. Night and 24 h ABPM diastolic BP values were lower than HBPM and OBPM values, while day 24 h ABPM values were slightly higher than HBPM and OBPM values. ABPM provides different BP values than OBPM and HBPM. Target BP for ABPM in high-risk pregnancy hypertension should be estimated based on the predictive value of adverse pregnancy outcomes

Study of influence of domain structure on observed magnetoresistance anomalies in GaMnAs

Magneto-transport properties of a Ga0.93Mn0.07As ferromagnetic semiconductor film with strong epitaxial strain (Ga0.7In0.3As buffer) have been studied. The observed magnetoresistance showed peculiar peaks at the magnetic fields corresponding to magnetization switching probed by Hall voltage. Computer simulations showed that these anomalies could originate from the formation of complex, island-like magnetic domains, and their propagation in the sample

Diagnostic value of potassium level in a spot urine sample as an index of 24-hour urinary potassium excretion in unselected patients hospitalized in a hypertension unit

<div><p>Background</p><p>Primary hyperaldosteronism may be associated with elevated 24-hour urinary potassium excretion. We evaluated the diagnostic value of spot urine (SU) potassium as an index of 24-hour urinary potassium excretion.</p><p>Methods</p><p>We measured SU and 24-hour urinary collection potassium and creatinine in 382 patients. Correlations between SU and 24-hour collections were assessed for potassium levels and potassium/creatinine ratios. We used the PAHO formula to estimate 24-hour urinary potassium excretion based on SU potassium level. The agreement between estimated and measured 24-hour urinary potassium excretion was evaluated using the Bland-Altman method. To evaluate diagnostic performance of SU potassium, we calculated areas under the curve (AUC) for SU potassium/creatinine ratio and 24-hour urinary potassium excretion estimated using the PAHO formula.</p><p>Results</p><p>Strongest correlation between SU and 24-hour collection was found for potassium/creatinine ratio (r = 0.69, P<0.001). The PAHO formula underestimated 24-hour urinary potassium excretion by mean 8.3±18 mmol/d (95% limits of agreement -28 to +44 mmol/d). Diagnostic performance of SU potassium/creatinine ratio was borderline good only if 24-hour urinary potassium excretion was largely elevated (AUC 0.802 for 120 mmol K⁺/24 h) but poor with lower values (AUC 0.696 for 100 mmol K⁺/24 h, 0.636 for 80 mmol K⁺/24 h, 0.675 for 40 mmol K⁺/24 h). Diagnostic performance of 24-hour urinary potassium excretion estimated by the PAHO formula was excellent with values above 120 mmol/d and good with lower values (AUC 0.941 for 120 mmol K⁺/24 h, 0.819 for 100 mmol K⁺/24 h, 0.823 for 80 mmol K⁺/24 h, 0.836 for 40 mmol K⁺/24 h).</p><p>Conclusions</p><p>Spot urine potassium/creatinine ratio might be a marker of increased 24-hour urinary potassium excretion and a potentially useful screening test when reliable 24-hour urine collection is not available. The PAHO formula allowed estimation of the 24-hour urinary potassium excretion based on SU measurements with reasonable clinical accuracy.</p></div

Receiver-operating characteristic (ROC) curves for the estimated 24-hour urinary potassium excretion.

<p>The ROC curve for cut-off 24-hour urinary potassium excretion of 60 mmol/24 h was omitted for clarity. AUC, area under the curve.</p

Correlations between spot urine and 24-hour urinary potassium measurements.

<p>1a: Potassium level in the spot urine sample vs. potassium level in the 24-hour urine collection (r = 0.47, P<0.001). 1b: Potassium level in the spot urine sample vs. 24-hour urinary potassium excretion (r = 0.28, P<0.001). 1c: Potassium/creatinine ratio in the spot urine sample vs. 24-hour urinary potassium excretion (r = 0.38, P<0.001). 1d: Potassium/creatinine ratio in the spot urine sample vs. 24-hour urinary potassium/creatinine ratio (r = 0.69, P<0.001).</p

Galvanomagnetic methods of Curie temperature determination in (Ga,Mn)As

We critically discuss various experimental methods to determine Curie temperature TC of (Ga,Mn)As thin layers or other conducting magnetic materials by means of electric charge transport measurements. They all base on the influence of sample magnetization on the magnetoresistivity tensor ρ̂ and are an alternative to the method based upon an analysis of the temperature derivative of the sample resistance (Novák et al., 2008). These methods can be applied even when standard SQUID magnetometers are difficult or impossible to use – for example for extremely small samples or in the case of experiments performed at very specific physical conditions, e.g. at high hydrostatic pressure inside the clamp cell. We show that the use of the so called Arrott plot prepared with the use of high magnetic field isotherms ρxx(H0),ρxy(H0) (H0 – external magnetic field) may lead to substantial (of the order of 10 K) divergence of the obtained TC values depending on the assumptions which are necessary to make in this case and depending on the direction of a magnetic anisotropy easy axis. We also propose a number of ways how to obtain, basing on low magnetic field isotherms ρxx(H0),ρxy(H0), clear and characteristic features which are closely related to the ferromagnetic–paramagnetic phase transition

The Bland-Altman plot.

<p>The Bland-Altman plot showing the difference between measured and estimated (PAHO formula) 24-hour urinary potassium excretion plotted against the mean 24-hour urinary potassium excretion by the two methods (mmol/d). Dashed lines indicate 95% limits of agreement (±1.96 SD).</p

Study group characteristics.

<p>Study group characteristics.</p