Forest Return on an Abandoned Field - Secondary Succession Under Monitored Conditions

The secondary succession pattern observed on an arable field abandoned since 1974 in Tilio-Carpinetum habitat is described and disscussed. Results obtained during 36 years of study confirm that succession on an abandoned field leads from a typical segetal community to the formation of a juvenile treestand composed of pioneer species. Our study supports the view that succession is a process which is largely dependent on the initial conditions and surrounding vegetation. The results indicate that some species can modify the course of this process, accelerating or slowing it down. Limitations of the method and prognosis of future vegetation development are also discussed

Electrically controlled spin-transistor operation in helical magnetic field

A proposal of electrically controlled spin transistor in helical magnetic field is presented. In the proposed device, the transistor action is driven by the Landau-Zener transitions that lead to a backscattering of spin polarized electrons and switching the transistor into the high-resistance state (off state). The on/off state of the transistor can be controlled by the all-electric means using Rashba spin-orbit coupling that can be tuned by the voltages applied to the side electrodes.Comment: 5 pages, 6 figure

Spin transistor operation driven by the Rashba spin-orbit coupling in the gated nanowire

The theoretical description has been proposed for the operation of the spin transistor in the gate-controlled InAs nanowire. The calculated current-voltage characteristics show that the current flowing from the source (spin injector) to the drain (spin detector) oscillates as a function of the gate voltage, which results from the precession of the electron spin caused by the Rashba spin-orbit interaction in the vicinity of the gate. We have studied two operation modes of the spin transistor: (A) the ideal operation mode with the full spin polarization of electrons in the contacts, the zero temperature, and the single conduction channel corresponding to the lowest-energy subband of the transverse motion and (B) the more realistic operation mode with the partial spin polarization of the electrons in the contacts, the room temperature, and the conduction via many transverse subbands taken into account. For mode (A) the spin-polarized current can be switched on/off by the suitable tuning of the gate voltage, for mode (B) the current also exhibits the pronounced oscillations but with no-zero minimal values. The computational results obtained for mode (B) have been compared with the recent experimental data and a good agreement has been found.Comment: 8 pages, 11 figure

Spin filter effect at room temperature in GaN/GaMnN ferromagnetic resonant tunneling diode

We have investigated the spin current polarization without the external magnetic field in the resonant tunneling diode with the emitter and quantum well layers made from the ferromagnetic GaMnN. For this purpose we have applied the self-consistent Wigner-Poisson method and studied the spin-polarizing effect of the parallel and antiparallel alignment of the magnetization in the ferromagnetic layers. The results of our calculations show that the antiparallel magnetization is much more advantageous for the spin filter operation and leads to the full spin current polarization at low temperatures and 35 % spin polarization of the current at room temperature.Comment: 4 pages, 5 figure

Record extension for short-gauged water quality parameters using a newly proposed robust version of the Line of Organic Correlation technique

In many situations the extension of hydrological or water quality time series at short-gauged stations is required. Ordinary least squares regression (OLS) of any hydrological or water quality variable is a traditional and commonly used record extension technique. However, OLS tends to underestimate the variance in the extended records, which leads to underestimation of high percentiles and overestimation of low percentiles, given that the data are normally distributed. The development of the line of organic correlation (LOC) technique is aimed at correcting this bias. On the other hand, the Kendall-Theil robust line (KTRL) method has been proposed as an analogue of OLS with the advantage of being robust in the presence of outliers. Given that water quality data are characterised by the presence of outliers, positive skewness and non-normal distribution of data, a robust record extension technique is more appropriate. In this paper, four record-extension techniques are described, and their properties are explored. These techniques are OLS, LOC, KTRL and a new technique proposed in this paper, the robust line of organic correlation technique (RLOC). RLOC includes the advantage of the LOC in reducing the bias in estimating the variance, but at the same time it is also robust in the presence of outliers. A Monte Carlo study and empirical experiment were conducted to examine the four techniques for the accuracy and precision of the estimate of statistical moments and over the full range of percentiles. Results of the Monte Carlo study showed that the OLS and KTRL techniques have serious deficiencies as record-extension techniques, while the LOC and RLOC techniques are nearly similar. However, RLOC outperforms OLS, KTRL and LOC when using real water quality records