The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform
H. Huitema - One of the best experts on this subject based on the ideXlab platform.
-
The importance of linear landscape elements for the pipistrellePipistrellus pipistrellus and the serotine batEptesicus serotinus
Landscape Ecology, 1997Co-Authors: B. Verboom, H. HuitemaAbstract:The relation between two species of bats, the pipistrelle ( Pipistrellus pipistrellus (Schreber, 1774)) and the serotine ( Eptesicus serotinus (Schreber, 1774)) and linear landscape elements such as hedgerows, tree lines and tree lanes was studied in an agricultural area in The Netherlands. The pipistrelle was observed almost entirely close to landscape elements, while serotines more frequently Crossed Fields and meadows. Serotine activity in these open areas was, however, negatively related to the distance to a landscape element and to windspeed. On a landscape scale the results indicate a more than proportional positive relation between the density of serotine bats and the density of linear landscape elements, whereas this relation was only proportional in the case of the pipistrelle. It is argued, that landscapes with a high density of linear elements have a surplus value for serotine bats. Three possible functions of linear elements for bats (orientation clues, foraging habitat and shelter from wind and/or predators) are discussed. Any of these may explain the results of this study.
-
The importance of linear landscape elements for the pipistrelle Pipistrellus pipistrellus and the serotine bat Eptesicus serotinus
Landscape Ecology, 1997Co-Authors: B. Verboom, H. HuitemaAbstract:The relation between two species of bats, the pipistrelle (Pipistrellus pipistrellus (Schreber, 1774)) and the serotine (Eptesicus serotinus (Schreber, 1774)) and linear landscape elements such as hedgerows, tree lines and tree lanes was studied in an agricultural area in The Netherlands. The pipistrelle was observed almost entirely close to landscape elements, while serotines more frequently Crossed Fields and meadows. Serotine activity in these open areas was, however, negatively related to the distance to a landscape element and to windspeed.
D Dialetis - One of the best experts on this subject based on the ideXlab platform.
-
theory of electron multipactor in Crossed Fields
Physics of Plasmas, 1995Co-Authors: Spilios Riyopoulos, David Chernin, D DialetisAbstract:A general theory of multipactor in orthogonal electric and magnetic Fields is given. The model consists of two parallel plates of known secondary emission properties, across which a time varying voltage is applied, and between which a constant magnetic field is applied. Expressions are derived for the resonant phases at which the RF‐driven cascades occur; these reduce to previously derived expressions in the limit of the vanishing magnetic field. In addition, this work obtains the conditions governing the stability of the motion about those phases, as well as a dynamic constraint from imposing the restriction that each impact on a plate is the first impact that is allowed by the equations of motion. Chaotic effects from the random ejection velocities of the secondaries are addressed for the first time. It is proven that the phase focusing effect from the radio frequency (RF) interaction will overcome the dispersive effect from the random emission, provided that the mean square emission velocity is suffici...
-
theory of electron multipactor in Crossed Fields
International Conference on Plasma Science, 1995Co-Authors: Spilios Riyopoulos, David Chernin, D DialetisAbstract:Summary form only given. A general theory of multipactor between parallel capacitor plates with orthogonal electric and magnetic Fields is given. Expressions are derived for the resonant phases at which the rf-driven cascades occur; these reduce to previously derived expressions in the limit of vanishing magnetic field. This work also obtains the conditions governing the stability of the motion about those phases, as well as a dynamic constraint from imposing the restriction that each impact on a plate is the first impact that is allowed by the equations of motion. Chaotic effects from the random ejection velocities of the secondaries are addressed for the first time.
S D Hogan - One of the best experts on this subject based on the ideXlab platform.
-
preparation of circular rydberg states in helium with n 70 using a modified version of the Crossed Fields method
Physical Review A, 2018Co-Authors: A A Morgan, V Zhelyazkova, S D HoganAbstract:Circular Rydberg states with $n=70$ have been prepared in helium using a modified version of the Crossed-Fields method. This approach to the preparation of high-$n$ circular Rydberg states overcomes limitations of the standard Crossed-Fields method which arise at this, and higher, values of $n$. The experiments were performed with atoms traveling in pulsed supersonic beams that were initially laser photoexcited from the metastable 1s2s$\,^3$S$_1$ level to the 1s73s$\,^3$S$_1$ level by resonance-enhanced two-color two-photon excitation in a magnetic field of 16.154 G. These excited atoms were then polarized using a perpendicular electric field of 0.844~V/cm, and transferred by a pulse of microwave radiation to the state that, when adiabatically depolarized, evolves into the $n=70$ circular state in zero electric field. The excited atoms were detected by state-selective electric field ionization. Each step of the circular state preparation process was validated by comparison with the calculated atomic energy level structure in the perpendicular electric and magnetic Fields used. Of the atoms initially excited to the 1s73s$\,^3$S$_1$ level, $\sim80$\% were transferred to the $n=70$ circular state. At these high values of $n$, $\Delta n = 1$ circular-to-circular Rydberg state transitions occur at frequencies below 20 GHz. Consequently, atoms in these states, and the circular state preparation process presented here, are well suited to hybrid cavity QED experiments with Rydberg atoms and superconducting microwave circuits.
-
preparation of circular rydberg states in helium using the Crossed Fields method
Physical Review A, 2016Co-Authors: V Zhelyazkova, S D HoganAbstract:Helium atoms have been prepared in the circular |n=55,l=54,ml=+54⟩ Rydberg state using the Crossed electric and magnetic Fields method. The atoms, initially traveling in pulsed supersonic beams, were photoexcited from the metastable 1s2sS13 level to the outermost, ml=0 Rydberg-Stark state with n=55 in the presence of a strong electric field and weak perpendicular magnetic field. Following excitation, the electric field was adiabatically switched off causing the atoms to evolve into the circular state with ml=+54 defined with respect to the magnetic-field quantization axis. The circular states were detected by ramped electric-field ionization along the magnetic-field axis. The dependence of the circular state production efficiency on the strength of the excitation electric field, and the electric-field switch-off time was studied, and microwave spectroscopy of the circular-to-circular |55,54,+54⟩→|56,55,+55⟩ transition at ∼38.5 GHz was performed.
-
high lying rydberg states of barium in Crossed Fields
Journal of Physics B, 2004Co-Authors: A M Abdulla, S D Hogan, Mingsheng Zhan, Jeanpatrick ConneradeAbstract:We report recent experimental developments in the study of high-lying Rydberg states of atomic barium in Crossed external electric and magnetic Fields. By employing a new, high resolution, pulsed laser system in conjunction with the experimental geometry we have previously used, we have been able to extend our investigations closer to the semiclassical limit. We have compiled Stark maps which clearly indicate changes in dynamics that take place as the electric field strength is increased for a fixed magnetic field strength of 1 T. We comment on these changes and draw comparisons with those observed previously at lower principal quantum number, lower spectral resolution and higher magnetic field strength.
B. Verboom - One of the best experts on this subject based on the ideXlab platform.
-
The importance of linear landscape elements for the pipistrellePipistrellus pipistrellus and the serotine batEptesicus serotinus
Landscape Ecology, 1997Co-Authors: B. Verboom, H. HuitemaAbstract:The relation between two species of bats, the pipistrelle ( Pipistrellus pipistrellus (Schreber, 1774)) and the serotine ( Eptesicus serotinus (Schreber, 1774)) and linear landscape elements such as hedgerows, tree lines and tree lanes was studied in an agricultural area in The Netherlands. The pipistrelle was observed almost entirely close to landscape elements, while serotines more frequently Crossed Fields and meadows. Serotine activity in these open areas was, however, negatively related to the distance to a landscape element and to windspeed. On a landscape scale the results indicate a more than proportional positive relation between the density of serotine bats and the density of linear landscape elements, whereas this relation was only proportional in the case of the pipistrelle. It is argued, that landscapes with a high density of linear elements have a surplus value for serotine bats. Three possible functions of linear elements for bats (orientation clues, foraging habitat and shelter from wind and/or predators) are discussed. Any of these may explain the results of this study.
-
The importance of linear landscape elements for the pipistrelle Pipistrellus pipistrellus and the serotine bat Eptesicus serotinus
Landscape Ecology, 1997Co-Authors: B. Verboom, H. HuitemaAbstract:The relation between two species of bats, the pipistrelle (Pipistrellus pipistrellus (Schreber, 1774)) and the serotine (Eptesicus serotinus (Schreber, 1774)) and linear landscape elements such as hedgerows, tree lines and tree lanes was studied in an agricultural area in The Netherlands. The pipistrelle was observed almost entirely close to landscape elements, while serotines more frequently Crossed Fields and meadows. Serotine activity in these open areas was, however, negatively related to the distance to a landscape element and to windspeed.
I.s. Kulagin - One of the best experts on this subject based on the ideXlab platform.
-
observation of the second mode of the multipactor discharge in Crossed Fields
Radiophysics and Quantum Electronics, 2019Co-Authors: E.v. Ilyakov, I.s. Kulagin, A S ShevchenkoAbstract:We detect the second discharge mode in the process of experimental studies of a one-sided multipactor discharge in Crossed Fields (microwave electric field and magnetostatic field) in the three-centimeter wavelength band in a rectangular waveguide and a cylindrical resonator cavity. In accordance with the theory, the intensity of the discharge at the second mode was slightly lower than that at the fundamental mode. However, it is still sufficient for initiation of microwave breakdowns, absorption of a significant fraction of the radiation power, and modification of the resonance frequency of the cavity.
-
A Multipactor Discharge in Crossed Fields Under the Conditions of a Combination of Two Waves with Close Frequencies
Radiophysics and Quantum Electronics, 2013Co-Authors: E.v. Ilyakov, I.s. KulaginAbstract:We study the multipactor discharge in Crossed Fields, specifically, a microwave electric field and a quasistatic magnetic field. The multipactor occurs under the conditions of superposition of two microwave pulses with close frequencies, which correspond to the three-centimeter wavelength range. Experiments in the rectangular waveguide demonstrate that the multipactor develops and exists in a wide range of differences in the signal frequencies, which covers on interval of up to 700 MHz. The specific power absorbed in the discharge is equal to several kW/cm^2, and the radiation is absorbed efficiently at both frequencies. When the signal power is initially insufficient to ensure the multipactor development, an additional signal at a close frequency allows one to switch the discharge, which absorbs microwaves efficiently, on and off. At a frequency difference of up to 40 MHz, the achieved switch-on time is about 100 ns. Switch-on of the second signal in the line with a resonator cavity, which has a frequency belonging to the cavity frequency band, also results in the discharge development and switches the cavity from the transition regime to the reflection regime.
-
Multipactor discharge in Crossed Fields in a cylindrical cavity for the 3-cm wavelength band
Radiophysics and Quantum Electronics, 2012Co-Authors: A. A. Vikharev, S. V. Kuzikov, E.v. Ilyakov, I.s. KulaginAbstract:We present the results of an experimental study of the one-sided multipactor discharge in Crossed Fields, namely, a dc magnetic field and a high-frequency electric field, in a cylindrical cavity at the TM011 mode in the 3-cm wavelength band. It is found that the discharge can develop in about 15 ns. In this case, the electron number density can reach values which are comparable with critical ones for this radiation frequency. As a result of the discharge evolution, the cavity switches from the regime of signal transmission to that of signal reflection. In this case, the maximum specific power dissipated by the discharge in the cavity walls can amount to several kilowatts per square centimeter.
-
The multipactor discharge in Crossed Fields in a rectangular waveguide of the 3-cm wavelength band
Radiophysics and Quantum Electronics, 2012Co-Authors: E.v. Ilyakov, I.s. KulaginAbstract:We present the results of an experimental study of a single-sided multipactor discharge in Crossed Fields in a rectangular waveguide of the 3-cm wavelength band. The discharges with the electron drift on the wide wall of the waveguide along and across the waveguide axis in a standing wave and a traveling wave are studied. It is found that the multipactor discharge is capable of developing and absorbing radiation intensively, if the microwave field is not uniform, and multiplying electrons can have only a limited number (20–30) of sequential collisions on the surface intervals between the field nodes. The specific power absorbed in the discharge amounted to several kilowatts per square centimeter for a microwave field of about 30 kV/cm. The obtained data allow one to predict the existence of the discharge in the waveguides and cavities of the devices, in which spatially developed volume modes are deployed to transport higher-power radiation including the modes with complicated structures of the microwave field, where the azimuthal distance between the field nodes is comparable with the length, at which the discharge saturates. The evaluations made show that the density of electrons in the discharge is approximately equal to the critical value for the used radiation frequency. The demonstrated properties of the multipactor discharge can be employed to develop absorbing devices and control the cavity properties.
-
Experimental study of a saturated multipactor in Crossed Fields
Radiophysics and Quantum Electronics, 2009Co-Authors: E.v. Ilyakov, I.s. Kulagin, V. E. NechaevAbstract:We propose an experimental scheme of and develop a method for studying a one-sided multipactor discharge in Crossed Fields in the saturation regime. Basic parameters of the discharge have been measured. In the experiment performed in a 3-cm wavelength band, the discharge develops in microwave Fields with intensities from 8 kV/cm (near the lower threshold) to 20 kV/cm and became stabilized during at least a hundred cycles of multiplication of secondary electrons on the discharge surface. In this case, the maximum power absorbed in the discharge amounts up to 4 kW/cm^2, and the corresponding density of the saturated-discharge current, up to 10 A/cm^2. The measured time of discharge development is equal to 15–30 ns. These parameters agree well with estimating calculations based on approximate analytical models.