911 research outputs found
A Radio Determination of the Time of the New Moon
The detection of the New Moon at sunset is of importance to communities based
on the lunar calendar. This is traditionally undertaken with visual
observations. We propose a radio method which allows a higher visibility of the
Moon relative to the Sun and consequently gives us the ability to detect the
Moon much closer to the Sun than is the case of visual observation. We first
compare the relative brightness of the Moon and Sun over a range of possible
frequencies and find the range 5--100\,GHz to be suitable. The next
consideration is the atmospheric absorption/emission due to water vapour and
oxygen as a function of frequency. This is particularly important since the
relevant observations are near the horizon. We show that a frequency of GHz is optimal for this programme. We have designed and constructed a
telescope with a FWHM resolution of 0.6 and low sidelobes to
demonstrate the potential of this approach. At the time of the 21 May 2012 New
Moon the Sun/Moon brightness temperature ratio was in agreement
with predictions from the literature when combined with the observed sunspot
numbers for the day. The Moon would have been readily detectable at from the Sun. Our observations at 16\,hr\,36\,min UT indicated that
the Moon would have been at closest approach to the Sun 16\,hr\,25\,min
earlier; this was the annular solar eclipse of 00\,hr\,00\,min\,UT on 21 May
2012.Comment: 11 pages, 15 figures, accepted for publication in MNRA
Assessment of mixing efficiency in a planar passive micromixer With t-shaped configuration
Microfluidic devices have garnered considerable interest owing to their prospective utilization in diverse domains, encompassing chemical synthesis, biological analysis, and medicinal research. Micromixers are critical in adequate fluid mixing at a microscale within the array of devices under consideration. This study aims to offer a comprehensive analysis of the efficacy of the T-shaped micromixer configuration in scenarios that necessitate accurate and expeditious mixing. This study examines the performance of a T micromixer through simulation and analysis. The findings demonstrate that T micromixers exhibit some drawbacks that result in suboptimal mixing efficiency. The attainment of a desirable level of mixing efficiency can be accomplished by utilizing splitting-recombination and chaotic advection mechanisms. The study's outcomes indicate that the T micromixer demonstrates its maximum mixing effectiveness, roughly 60% when the Reynolds number (Re) is at or below 0.5. Nevertheless, it has been observed that the T micromixer encounters a decrease in mixing effectiveness as the Reynolds number escalates within the range of 0.5 to 15.</p
From Gapped Excitons to Gapless Triplons in One Dimension
Often, exotic phases appear in the phase diagrams between conventional
phases. Their elementary excitations are of particular interest. Here, we
consider the example of the ionic Hubbard model in one dimension. This model is
a band insulator (BI) for weak interaction and a Mott insulator (MI) for strong
interaction. Inbetween, a spontaneously dimerized insulator (SDI) occurs which
is governed by energetically low-lying charge and spin degrees of freedom.
Applying a systematically controlled version of the continuous unitary
transformations (CUTs) we are able to determine the dispersions of the
elementary charge and spin excitations and of their most relevant bound states
on equal footing. The key idea is to start from an externally dimerized system
using the relative weak interdimer coupling as small expansion parameter which
finally is set to unity to recover the original model.Comment: 18 pages, 10 figure
Excitation Spectrum of One-dimensional Extended Ionic Hubbard Model
We use Perturbative Continuous Unitary Transformations (PCUT) to study the
one dimensional Extended Ionic Hubbard Model (EIHM) at half-filling in the band
insulator region. The extended ionic Hubbard model, in addition to the usual
ionic Hubbard model, includes an inter-site nearest-neighbor (n.n.) repulsion,
. We consider the ionic potential as unperturbed part of the Hamiltonian,
while the hopping and interaction (quartic) terms are treated as perturbation.
We calculate total energy and ionicity in the ground state. Above the ground
state, (i) we calculate the single particle excitation spectrum by adding an
electron or a hole to the system. (ii) the coherence-length and spectrum of
electron-hole excitation are obtained. Our calculations reveal that for V=0,
there are two triplet bound state modes and three singlet modes, two anti-bound
states and one bound state, while for finite values of there are four
excitonic bound states corresponding to two singlet and two triplet modes. The
major role of on-site Coulomb repulsion is to split singlet and triplet
collective excitation branches, while tends to pull the singlet branches
below the continuum to make them bound states.Comment: 10 eps figure
Critical design factors on performance of car jack lifting operations
Car jack is an equipped accessory package in every units of car sold to customer that used to uplift the cars while replacing tires during an emergency or repair. The automotive manufacturers are actively conducting their Product Improvement Campaign and the objective of the campaign is to improve the quality of product sold to the customers. The current jack design has a possibility of failure during its operations. The customer satisfaction point of view will be converted to engineering characteristic to acquire the concept of design and input into new design proposal and at the same time eliminate the possibility of failure of the current design. The research is conducted to improve the current jack design on its performance in lifting operations. The scope of research is to identify the critical zone in jack design structure that possibly causing the failure during its operations. To optimize the existing design, it is proposed some modification on the jack structure with a minimum weight increment but improve the design structural strength. The failure root cause analysis, reliability test and Design Failure Mode and Effect Analysis have been used to identify the specific critical area in the structure and resolve them by proposing the new improved jack design. The current car jack sample in market is used as an industrial sample for design analysis to find the target area for further improvement. From the analysis, we can know the critical design factors in the current car jack design and the required design improvement to enhance its performance in lifting operations
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