8,899 research outputs found
The DRIFT Directional Dark Matter Detector and First Studies of the Head-Tail Effect
Measurement of the direction of the elastic nuclear recoil track and
ionization charge distribution along it, gives unique possibility for
unambiguous detection of the dark matter WIMP particle. Within current
radiation detection technologies only Time Projection Chambers filled with low
pressure gas are capable of such measurement. Due to the character of the
electronic and nuclear stopping powers of low energy nuclear recoils in the
gas, an asymmetric ionization charge distribution along their tracks may be
expected. Preliminary study of this effect, called Head-Tail, has been carried
out here using the SRIM simulation program for Carbon and Sulfur in 40 Torr
carbon disulfide, as relevant to the DRIFT detector. Investigations were
focused on ion tracks projected onto the axis of the initial direction of
motion in the energy range between 10 and 400 keV. Results indicate the likely
existence of an asymmetry influenced by two competing effects: the nature of
the stopping power and range straggling. The former tends to result in the Tail
being greater than the Head and the latter the reverse. It has been found that
for projected tracks the mean position of the ionization charge flows from
'head' to 'tail' with the magnitude depending on the ion type and its energy.Comment: To appear in the proceedings of Dark 2007 Sixth International
Heidelberg conference on "Dark Matter in Astro & Particle Physics", Sydney,
Australia 24th-28th September 200
Measurement of the Scintillation Efficiency of Na Recoils in NaI(Tl) down to 10 keV Nuclear Recoil Energy relevant to Dark Matter Searches
We present preliminary results of measurements of the quenching factor for Na
recoils in NaI(Tl) at room temperature, made at a dedicated neutron facility at
the University of Sheffield. Measurements have been performed with a 2.45 MeV
mono-energetic neutron generator in the energy range from 10 keV to 100 keV
nuclear recoil energy. A BC501A liquid scintillator detector was used to tag
neutrons. Cuts on pulse-shape discrimination from the BC501A liquid
scintillator detector and neutron time-of-flight were performed on pulses
recorded by a digitizer with a 2 ns sampling time. Measured quenching factors
range from 19% to 26%, in agreement with other experiments. From pulse-shape
analysis, a mean time of pulses from electron and nuclear recoils are compared
down to 2 keV electron equivalent energy.Comment: to appear in Proc. 6th Int. Workshop on the Identification of Dark
Matter, 11-16 September 2006, Rhodes, Greece; 6 pages, 4 figures; corrected
preliminary theoretical estimation curve plotted in figure
Forces and atomic relaxations in the pSIC approach with ultrasoft pseudopotentials
We present the scheme that allows for efficient calculations of forces in the
framework of pseudopotential self-interaction corrected (pSIC) formulation of
the density functional theory. The scheme works with norm conserving and also
with ultrasoft pseudopotentials and has been implemented in the plane-wave
basis code {\sc quantum espresso}. We have performed tests of the internal
consistency of the derived expressions for forces considering ZnO and CeO
crystals. Further, we have performed calculations of equilibrium geometry for
LaTiO, YTiO, and LaMnO perovskites and also for Re and Mn pairs in
silicon. Comparison with standard DFT and DFT+U approaches shows that in the
cases where spurious self-interaction matters, the pSIC approach predicts
different geometry, very often closer to the experimental data.Comment: 11 pages, 2 figure
Origin of bulk uniaxial anisotropy in zinc-blende dilute magnetic semiconductors
It is demonstrated that the nearest neighbor Mn pair on the GaAs (001)
surface has a lower energy for the [-110] direction comparing to the [110]
case. According to the group theory and the Luttinger's method of invariants,
this specific Mn distribution results in bulk uniaxial in-plane and
out-of-plane anisotropies. The sign and magnitude of the corresponding
anisotropy energies determined by a perturbation method and ab initio
computations are consistent with experimental results.Comment: 5 pages, 1 figur
Influence of band structure effects on domain-wall resistance in diluted ferromagnetic semiconductors
Intrinsic domain-wall resistance (DWR) in (Ga,Mn)As is studied theoretically
and compared to experimental results. The recently developed model of spin
transport in diluted ferromagnetic semiconductors [Van Dorpe et al., Phys. Rev.
B 72, 205322 (2005)] is employed. The model combines the disorder-free
Landauer-B\"uttiker formalism with the tight-binding description of the host
band structure. The obtained results show how much the spherical 4x4 kp model
[Nguyen, Shchelushkin, and Brataas, cond-mat/0601436] overestimates DWR in the
adiabatic limit, and reveal the dependence of DWR on the magnetization profile
and crystallographic orientation of the wall.Comment: 4 pages, 4 figures, submitted to Phys. Rev. B - Rapid Com
ΠΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΠ΅ Ρ Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΡΡΠΈΠΊΠΈ ΡΠΌΠΊΠΎΡΡΠ½ΡΡ Π΄Π°ΡΡΠΈΠΊΠΎΠ² Π²Π»Π°ΠΆΠ½ΠΎΡΡΠΈ
The sensor design features and the sensing material properties which can influence the response time of the polymer-based capacitive humidity sensors are shortly discussed. The ways of specifying the dynamic properties of capacitive humidity sensors in technical data sheets by the leading companies on the market are briefly characterized and discussed.The schematic view and operation of the experimental setup for determining of the dynamic parameters of capacitive humidity sensors at different temperatures of humid air are described. The dynamic behaviour of polymer-based capacitive humidity sensors was registered as the measurement profiles for both positive and negative step changes in humidity level. The response and recovery times, as well as the time constants for the exponential approximation fits of the step responses, were determined either graphically or analytically, based on the collected data.The changes of these parameters under atmospheric pressure within the temperature range fromΒ βΒ 30 Β°C to + 20 Β°C were analysed. The exemplary transient measurement profiles are shown, together with the illustrations of the graphical method for determining the response and recovery times. Also, the plots of the relationship between response and recovery times as well as time constants, and temperature, are presented. Some explanations of the obtained results are suggested.Π Π°ΡΡΠΌΠΎΡΡΠ΅Π½Ρ ΠΊΠΎΠ½ΡΡΡΡΠΊΡΠΈΠ²Π½ΡΠ΅ ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΡ ΠΈ ΡΠ²ΠΎΠΉΡΡΠ²Π° ΡΡΠ²ΡΡΠ²ΠΈΡΠ΅Π»ΡΠ½ΡΡ
ΠΌΠ°ΡΠ΅ΡΠΈΠ°Π»ΠΎΠ², Π²Π»ΠΈΡΡΡΠΈΠ΅ Π½Π° Π²ΡΠ΅ΠΌΡ ΠΎΡΠΊΠ»ΠΈΠΊΠ° ΡΠΌΠΊΠΎΡΡΠ½ΡΡ
Π΄Π°ΡΡΠΈΠΊΠΎΠ² Π²Π»Π°ΠΆΠ½ΠΎΡΡΠΈ Π½Π° ΠΎΡΠ½ΠΎΠ²Π΅ ΠΏΠΎΠ»ΠΈΠΌΠ΅ΡΠΎΠ². ΠΡΠΏΠΎΠ»Π½Π΅Π½ ΠΊΡΠ°ΡΠΊΠΈΠΉ ΠΎΠ±Π·ΠΎΡ ΠΈ Π°Π½Π°Π»ΠΈΠ· ΡΠΏΠΎΡΠΎΠ±ΠΎΠ² ΠΎΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΡ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΡ
Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΡΡΠΈΠΊ ΡΠΌΠΊΠΎΡΡΠ½ΡΡ
Π΄Π°ΡΡΠΈΠΊΠΎΠ² Π²Π»Π°ΠΆΠ½ΠΎΡΡΠΈ Π² ΡΠ΅Ρ
Π½ΠΈΡΠ΅ΡΠΊΠΎΠΉ Π΄ΠΎΠΊΡΠΌΠ΅Π½ΡΠ°ΡΠΈΠΈ Π²Π΅Π΄ΡΡΠΈΡ
ΠΏΡΠΎΠΈΠ·Π²ΠΎΠ΄ΠΈΡΠ΅Π»Π΅ΠΉ, ΠΏΡΠ΅Π΄ΡΡΠ°Π²Π»Π΅Π½Π½ΡΡ
Π½Π° ΡΡΠ½ΠΊΠ΅.ΠΡΠΈΠ²Π΅Π΄Π΅Π½ΠΎ ΠΎΠΏΠΈΡΠ°Π½ΠΈΠ΅ ΡΡ
Π΅ΠΌΡ ΠΈ ΡΠ°Π±ΠΎΡΡ ΡΠΊΡΠΏΠ΅ΡΠΈΠΌΠ΅Π½ΡΠ°Π»ΡΠ½ΠΎΠΉ ΡΡΡΠ°Π½ΠΎΠ²ΠΊΠΈ Π΄Π»Ρ ΠΎΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΡ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΡ
Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΡΡΠΈΠΊ ΡΠΌΠΊΠΎΡΡΠ½ΡΡ
Π΄Π°ΡΡΠΈΠΊΠΎΠ² Π²Π»Π°ΠΆΠ½ΠΎΡΡΠΈ ΠΏΡΠΈ ΡΠ°Π·Π»ΠΈΡΠ½ΡΡ
Π·Π½Π°ΡΠ΅Π½ΠΈΡΡ
ΡΠ΅ΠΌΠΏΠ΅ΡΠ°ΡΡΡΡ Π²Π»Π°ΠΆΠ½ΠΎΠ³ΠΎ Π²ΠΎΠ·Π΄ΡΡ
Π°. ΠΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΈΠ΅ Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΡΡΠΈΠΊΠΈ ΡΠΌΠΊΠΎΡΡΠ½ΡΡ
Π΄Π°ΡΡΠΈΠΊΠΎΠ² Π²Π»Π°ΠΆΠ½ΠΎΡΡΠΈ Π½Π° ΠΎΡΠ½ΠΎΠ²Π΅ ΠΏΠΎΠ»ΠΈΠΌΠ΅ΡΠΎΠ² ΠΎΠΏΡΠ΅Π΄Π΅Π»ΡΠ»ΠΈΡΡ Π² Π²ΠΈΠ΄Π΅ ΠΎΡΠΊΠ»ΠΈΠΊΠ° Π²ΡΡ
ΠΎΠ΄Π½ΠΎΠ³ΠΎ ΡΠΈΠ³Π½Π°Π»Π° ΠΏΡΠΈ ΡΡΡΠΏΠ΅Π½ΡΠ°ΡΠΎΠΌ ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΠΈ Π²Π»Π°ΠΆΠ½ΠΎΡΡΠΈ ΠΊΠ°ΠΊ Ρ ΠΏΠΎΠ»ΠΎΠΆΠΈΡΠ΅Π»ΡΠ½ΡΠΌ, ΡΠ°ΠΊ ΠΈ Ρ ΠΎΡΡΠΈΡΠ°ΡΠ΅Π»ΡΠ½ΡΠΌ ΡΠ°Π³ΠΎΠΌ. ΠΡΠ΅ΠΌΠ΅Π½Π° ΠΎΡΠΊΠ»ΠΈΠΊΠ° ΠΈ Π²ΠΎΡΡΡΠ°Π½ΠΎΠ²Π»Π΅Π½ΠΈΡ, Π° ΡΠ°ΠΊΠΆΠ΅ ΠΏΠΎΡΡΠΎΡΠ½Π½ΡΠ΅ Π²ΡΠ΅ΠΌΠ΅Π½ΠΈ Π΄Π»Ρ ΡΠΊΡΠΏΠΎΠ½Π΅Π½ΡΠΈΠ°Π»ΡΠ½ΠΎΠΉ Π°ΠΏΠΏΡΠΎΠΊΡΠΈΠΌΠ°ΡΠΈΠΈ ΠΎΡΠΊΠ»ΠΈΠΊΠ° Π½Π° ΡΡΡΠΏΠ΅Π½ΡΠ°ΡΠΎΠ΅ Π²ΠΎΠ·Π΄Π΅ΠΉΡΡΠ²ΠΈΠ΅, ΠΎΠΏΡΠ΅Π΄Π΅Π»ΡΠ»ΠΈΡΡ Π½Π° ΠΎΡΠ½ΠΎΠ²Π΅ ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΠΎΠ² ΠΈΠ·ΠΌΠ΅ΡΠ΅Π½ΠΈΠΉ Π³ΡΠ°ΡΠΈΡΠ΅ΡΠΊΠΈ Π»ΠΈΠ±ΠΎ Π°Π½Π°Π»ΠΈΡΠΈΡΠ΅ΡΠΊΠΈ.ΠΡΠΎΠ°Π½Π°Π»ΠΈΠ·ΠΈΡΠΎΠ²Π°Π½Ρ ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΡ ΡΠΊΠ°Π·Π°Π½Π½ΡΡ
ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΠΎΠ² Π² ΠΏΡΠ΅Π΄Π΅Π»Π°Ρ
ΡΠ΅ΠΌΠΏΠ΅ΡΠ°ΡΡΡ ΠΎΡ β 30 Β°Π‘ Π΄ΠΎ + 20 Β°Π‘ ΠΏΡΠΈ Π°ΡΠΌΠΎΡΡΠ΅ΡΠ½ΠΎΠΌ Π΄Π°Π²Π»Π΅Π½ΠΈΠΈ. ΠΡΠΈΠ²Π΅Π΄Π΅Π½Ρ ΠΏΡΠΈΠΌΠ΅ΡΡ ΠΏΠΎΠ»ΡΡΠ΅Π½Π½ΡΡ
ΠΏΠ΅ΡΠ΅Ρ
ΠΎΠ΄Π½ΡΡ
Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΡΡΠΈΠΊ, ΠΏΡΠΎΠΈΠ»Π»ΡΡΡΡΠΈΡΠΎΠ²Π°Π½ Π³ΡΠ°ΡΠΈΡΠ΅ΡΠΊΠΈΠΉ ΠΌΠ΅ΡΠΎΠ΄ ΠΎΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΡ Π²ΡΠ΅ΠΌΡΠ½ ΠΎΡΠΊΠ»ΠΈΠΊΠ° ΠΈ Π²ΠΎΡΡΡΠ°Π½ΠΎΠ²Π»Π΅Π½ΠΈΡ. ΠΡΠ΅Π΄ΡΡΠ°Π²Π»Π΅Π½Ρ Π³ΡΠ°ΡΠΈΠΊΠΈ Π·Π°Π²ΠΈΡΠΈΠΌΠΎΡΡΠΈ Π²ΡΠ΅ΠΌΡΠ½ ΠΎΡΠΊΠ»ΠΈΠΊΠ° ΠΈ Π²ΠΎΡΡΡΠ°Π½ΠΎΠ²Π»Π΅Π½ΠΈΡ, Π° ΡΠ°ΠΊΠΆΠ΅ ΠΏΠΎΡΡΠΎΡΠ½Π½ΡΡ
Π²ΡΠ΅ΠΌΠ΅Π½ΠΈ, ΠΎΡ ΡΠ΅ΠΌΠΏΠ΅ΡΠ°ΡΡΡΡ. ΠΡΠ΅Π΄Π»ΠΎΠΆΠ΅Π½Ρ Π²ΠΎΠ·ΠΌΠΎΠΆΠ½ΡΠ΅ ΠΎΠ±ΡΡΡΠ½Π΅Π½ΠΈΡ ΠΏΠΎΠ»ΡΡΠ΅Π½Π½ΡΡ
ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΠΎΠ²
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