171,247 research outputs found
X-ray background and its correlation with the 21 cm signal
We use high resolution hydrodynamical simulations to study the contribution
to the X-ray background from high- energetic sources, such as X-ray
binaries, accreting nuclear black holes and shock heated interstellar medium.
Adopting the model discussed in Eide et al. (2018), we find that these X-ray
sources during the Epoch of Reionization (EoR) contribute less than a few
percent of the unresolved X-ray background. The same sources contribute to less
than 2\% of the measured angular power spectrum of the fluctuations of
the X-ray background. The outputs of radiative transfer simulations modeling
the EoR are used to evaluate the cross-correlations of X-ray background with
the 21~cm signal from neutral hydrogen. Such correlation could be used to
confirm the origin of the 21 cm signal, as well as give information on the
properties of the X-ray sources during the EoR. We find that the correlations
are positive during the early stages of reionization when most of the hydrogen
is neutral, while they become negative when the intergalactic medium gets
highly ionized, with the transition from positive to negative depending on both
the X-ray model and the scale under consideration. With {\tt SKA} as the
reference instrument for the 21~cm experiment, the predicted S/N for such
correlations is if the corresponding X-ray survey is only able to resolve
and remove X-ray sources with observed flux , while the cumulative S/N from to at
is if sources with observed flux are detected.Comment: 9 pages, 8 figure
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Active noise control on high frequency narrow band dental drill noise: Preliminary results
Dental drills produce a characteristic noise that is uncomfortable for patients and is also known to be harmful to dentists under prolonged exposure. It is therefore desirable to protect the patient and dentist whilst allowing two-way communication. A solution is to use a combination of the three main noise cancellation methods, namely, Passive Noise Control, Adaptive Filtering and Active Noise Control. Dental drill noise occurs at very high frequency ranges in relation to conventional ANC, typically 2kHz to 6kHz and it has a narrow band characteristic due to the direct relation of the noise to the rotational speed of the bearing. This paper presents a design of an experimental rig where first applications of ANC on dental drill noise are executed using the standard filtered reference Least Mean Square (FXLMS) algorithm. The secondary path is kept as simple as possible, due to the high frequency range of interest, and hence is chosen as the space between headphone loudspeaker and error microphone placed in the ear (input of the headphone loudspeaker and the output of the error microphone). A standard headphone loudspeaker is used for the control source and the microphone inside of an âEar and Cheek Simulator Type 43AGâ is used as the error microphone. The secondary path transfer function is obtained and preliminary results of the application of ANC are discussed
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Dental drill noise reduction using a combination of active noise control, passive noise control and adaptive filtering
Dental drills produce a characteristic high frequency, narrow band noise that is uncomfortable for patients and is also known to be harmful to dentists under prolonged exposure. It is therefore desirable to protect the patient and dentist whilst allowing two-way communication. A solution is to use a combination of the three main noise control methods, namely, Passive Noise Control (PNC), Adaptive Filtering (AF) and Active Noise Control (ANC). This paper discusses the application of the three methods to reduce dental drill noise while allowing two-way communication. Experimental setup for measuring the noise reduction by PNC is explained and results from different headphones and headphone types are presented. The implementation and results of an AF system using the Least Mean Square (LMS) algorithm are shown. ANC requires a modification of the LMS algorithm due to the introduction of the electro-acoustical cancellation path transfer function to compensate for the delays introduced by the control system. Therefore a cancellation path transfer function modeling method based on the filtered reference LMS (FXLMS) algorithm is presented along with preliminary results of the implementation
A Note on Pretzelosity TMD Parton Distribution
We show that the transverse-momentum-dependent parton distribution, called as
Pretzelosity function, is zero at any order in perturbation theory of QCD for a
single massless quark state. This implies that Pretzelosity function is not
factorized with the collinear transversity parton distribution at twist-2, when
the struck quark has a large transverse momentum. Pretzelosity function is in
fact related to collinear parton distributions defined with twist-4 operators.
In reality, Pretzelosity function of a hadron as a bound state of quarks and
gluons is not zero. Through an explicit calculation of Pretzelosity function of
a quark combined with a gluon nonzero result is found.Comment: improved explanation, published version in Phys. Lett.
Renormalization group for the probability distribution of magnetic impurities in a random-field model
Extending the usual Ginzburg-Landau theory for the random-field Ising model,
the possibility of dimensional reduction is reconsidered. A renormalization
group for the probability distribution of magnetic impurities is applied. New
parameters corresponding to the extra coupling constants in the
replica Hamiltonian are introduced. Although they do not affect the critical
phenomena near the upper critical dimension, they can when dimensions are
lowered.Comment: 16 pages, 11 figures, revte
Measuring patchy reionisation with kSZ-21 cm correlations
We study cross-correlations of the kinetic Sunyaev-Zel'dovich effect (kSZ)
and 21 cm signals during the epoch of reionisation (EoR) to measure the effects
of patchy reionisation. Since the kSZ effect is proportional to the
line-of-sight velocity, the kSZ-21 cm cross correlation suffers from
cancellation at small angular scales. We thus focus on the correlation between
the kSZ-squared field (kSZ) and 21 cm signals. When the global ionisation
fraction is low (), the kSZ fluctuation is dominated by
rare ionised bubbles which leads to an anti-correlation with the 21 cm signal.
When , the correlation is dominated by small pockets of
neutral regions, leading to a positive correlation. However, at very high
redshifts when , the spin temperature fluctuations change the sign of
the correlation from negative to positive, as weakly ionised regions can have
strong 21 cm signals in this case. To extract this correlation, we find that
Wiener filtering is effective in removing large signals from the primary CMB
anisotropy. The expected signal-to-noise ratios for a 10-hour integration
of upcoming Square Kilometer Array data cross-correlated with maps from the
current generation of CMB observatories with 3.4~K arcmin noise and
1.7~arcmin beam over 100~deg are 51, 60, and 37 for , 0.5, and
0.9, respectively.Comment: 7pages, 7 figure
A Cosmic Microwave Background Radiation Polarimeter Using Superconducting Bearings
Measurements of the polarization of the cosmic microwave background (CMB)
radiation are expected to significantly increase our understanding of the early
universe. We present a design for a CMB polarimeter in which a cryogenically
cooled half wave plate rotates by means of a high-temperature superconducting
(HTS) bearing. The design is optimized for implementation in MAXIPOL, a
balloon-borne CMB polarimeter. A prototype bearing, consisting of commercially
available ring-shaped permanent magnet and an array of YBCO bulk HTS material,
has been constructed. We measured the coefficient of friction as a function of
several parameters including temperature between 15 and 80 K, rotation
frequency between 0.3 and 3.5 Hz, levitation distance between 6 and 10 mm, and
ambient pressure between 10^{-7} and 1 torr. The low rotational drag of the HTS
bearing allows rotations for long periods of time with minimal input power and
negligible wear and tear thus making this technology suitable for a future
satellite mission.Comment: 6 pages, IEEE-Transactions of Applied Superconductivity, 2003, Vol.
13, in pres
Will mobile video become the killer application for 3G? - an empirical model for media convergence
Mobile carriers have continually rolled out 3G mobile video applications to increase their revenue and profits. The presumption is that video is superior to the already successful SMS, ringtones, and pictures, and can create greater value to users. However, recent market surveys revealed contradicting results. Motivated by this discrepancy, we propose in this paper a parsimonious model for user acceptance of mobile entertainment as digital convergence. Integrating research on Information Systems, Flow, and Media Psychology, we take a unique approach to user acceptance of digital convergence - platform migration. Our key proposition is that the interaction between media types and the platform-specific constraints is the key determinant of user evaluation. Particularly, users' involvement in the media is determined by both the entertaining time span on the original platform and the attentional constraint of the new platform. The mismatch between the two spans can result in lower level involvement, which in turn cause no or even negative user emotional responses. The model was tested with empirical data. We discuss the theoretical contributions, strategic and design implications, and future research directions derived from this theoretical framewor
Distribution of the second virial coefficients of globular proteins
George and Wilson [Acta. Cryst. D 50, 361 (1994)] looked at the distribution
of values of the second virial coefficient of globular proteins, under the
conditions at which they crystallise. They found the values to lie within a
fairly narrow range. We have defined a simple model of a generic globular
protein. We then generate a set of proteins by picking values for the
parameters of the model from a probability distribution. At fixed solubility,
this set of proteins is found to have values of the second virial coefficient
that fall within a fairly narrow range. The shape of the probability
distribution of the second virial coefficient is Gaussian because the second
virial coefficient is a sum of contributions from different patches on the
protein surface.Comment: 5 pages, including 3 figure
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