3,793 research outputs found
An investigation on the energy recovery potential of sewage sludge in Malaysia through biogas generation
In a world where energy is being a primary concern, extracting energy from waste has been a common interest in world today which is striving for energy. The research title is ―An investigation on the energy recovery potential of sewage sludge in Malaysia through biogas generation”. This research will be focused mainly on recovering energy through biogas generation while using sewage sludge as the feed source. Sewage sludge is basically produced from the treatment of domestic wastewater and consists of two basic forms which is raw primary sludge (basically faecal material) and secondary sludge (a living ‗culture‘ of organisms that help remove contaminants from wastewater before it is returned to rivers or the sea). The material that remains after the digestion process is referred to as biosolids. The main purpose of coming up with this research is because the current cost of disposing sewage sludge in Malaysia is around 1billion ringgit annually. There is also very limited landfill land that is available now in Malaysia for the sludge disposal. Sludge cannot be dispose freely and need a proper disposal method as it contains bacteria and can cause health problem. Based on all this causes, this research concentrate on reducing the sludge content and at the same time extract energy from the waste which is in this case is sewage sludge. Based on the background study, anaerobic digestion method has been identified as the most efficient process that can be applied to recover energy from domestic sewage sludge and at the same time reduce the sludge content as well. This finding is explained in the report below. Anaerobic digestion is basically a natural process that occurs from the breakdown of organic material by micro-organisms in the absence of oxygen. This digestion process reduces the primary sludge content, and the byproduct of this will be biogas. In order to carry out this project, a simulation of anaerobic digestion plant will be designed using HYSYS simulation. In this research, this simulation will be studied thoroughly to get the most output from the applied feed rate. Later from the simulation the amounts of electrical energy that can be recovered from the biogas will be calculated. The outcome of this result will conclude the potential of recovering energy from sewage sludge. Therefore, this study of energy recovery potential through biogas generation by using sewage sludge becomes economically and ecologically attractive for us in Malaysia
Simultaneous multi-frequency single pulse observations of pulsars
We performed simultaneous observations at 326.5 MHz with the Ooty Radio
Telescope and at 326, 610 and 1308 MHz with the Giant Meterwave Radio Telescope
for a sample of 12 pulsars, where frequency dependent single pulse behaviour
was reported. The single pulse sequences were analysed with fluctuation
analysis, sensitive to both the average fluctuation properties (using longitude
resolved fluctuation spectrum and two-dimensional fluctuation spectrum) as well
as temporal changes in these (using sliding two-dimensional fluctuation
spectrum ) to establish concurrent changes in subpulse drifting over the
multiple frequencies employed. We report subpulse drifting in PSR J09345249
for the first time. We also report pulse nulling measurements in PSRs
J09345249, B1508+55, J18222256, B184519 and J19010906 for the first
time. Our measurements of subpulse drifting and pulse nulling for the rest of
the pulsars are consistent with previously reported values. Contrary to
previous belief, we find no evidence for a frequency dependent drift pattern in
PSR B2016+28 implied by non-simultaneous observations by Oster et al. (1977).
In PSRs B1237+25, J18222256, J19010906 and B204516, our longer and
more sensitive observations reveal multiple drift rates with distinct P3. We
increase the sample of pulsars showing concurrent nulling across multiple
frequencies by more than 100 percent, adding 4 more pulsars to this sample. Our
results confirm and further strengthen the understanding that the subpulse
drifting and pulse nulling are broadband consistent with previous studies
(Gajjar et al. 2014a; Rankin 1986; Weltevrede et al. 2007) and are closely tied
to physics of polar gap.Comment: 22 pages, 44 figures, Single pulse studies of pulsars, accepted by
A&
PONDER - A Real time software backend for pulsar and IPS observations at the Ooty Radio Telescope
This paper describes a new real-time versatile backend, the Pulsar Ooty Radio
Telescope New Digital Efficient Receiver (PONDER), which has been designed to
operate along with the legacy analog system of the Ooty Radio Telescope (ORT).
PONDER makes use of the current state of the art computing hardware, a
Graphical Processing Unit (GPU) and sufficiently large disk storage to support
high time resolution real-time data of pulsar observations, obtained by
coherent dedispersion over a bandpass of 16 MHz. Four different modes for
pulsar observations are implemented in PONDER to provide standard reduced data
products, such as time-stamped integrated profiles and dedispersed time series,
allowing faster avenues to scientific results for a variety of pulsar studies.
Additionally, PONDER also supports general modes of interplanetary
scintillation (IPS) measurements and very long baseline interferometry data
recording. The IPS mode yields a single polarisation correlated time series of
solar wind scintillation over a bandwidth of about four times larger (16 MHz)
than that of the legacy system as well as its fluctuation spectrum with high
temporal and frequency resolutions. The key point is that all the above modes
operate in real time. This paper presents the design aspects of PONDER and
outlines the design methodology for future similar backends. It also explains
the principal operations of PONDER, illustrates its capabilities for a variety
of pulsar and IPS observations and demonstrates its usefulness for a variety of
astrophysical studies using the high sensitivity of the ORT.Comment: 25 pages, 14 figures, Accepted by Experimental Astronom
Detection of long nulls in PSR B170616, a pulsar with large timing irregularities
Single pulse observations, characterizing in detail, the nulling behaviour of
PSR B170616 are being reported for the first time in this paper. Our regular
long duration monitoring of this pulsar reveals long nulls of 2 to 5 hours with
an overall nulling fraction of 312\%. The pulsar shows two distinct phases
of emission. It is usually in an active phase, characterized by pulsations
interspersed with shorter nulls, with a nulling fraction of about 15 \%, but it
also rarely switches to an inactive phase, consisting of long nulls. The nulls
in this pulsar are concurrent between 326.5 and 610 MHz. Profile mode changes
accompanied by changes in fluctuation properties are seen in this pulsar, which
switches from mode A before a null to mode B after the null. The distribution
of null durations in this pulsar is bimodal. With its occasional long nulls,
PSR B170616 joins the small group of intermediate nullers, which lie between
the classical nullers and the intermittent pulsars. Similar to other
intermediate nullers, PSR B170616 shows high timing noise, which could be
due to its rare long nulls if one assumes that the slowdown rate during such
nulls is different from that during the bursts.Comment: Accepted for publication in MNRA
Magnetic Field Structure and Stochastic Reconnection in a Partially Ionized Gas
We consider stochastic reconnection in a magnetized, partially ionized
medium. Stochastic reconnection is a generic effect, due to field line
wandering, in which the speed of reconnection is determined by the ability of
ejected plasma to diffuse away from the current sheet along magnetic field
lines, rather than by the details of current sheet structure. We consider the
limit of weak stochasticity, so that the mean magnetic field energy density is
greater than either the turbulent kinetic energy density or the energy density
associated with the fluctuating component of the field. We consider field line
stochasticity generated through a turbulent cascade, which leads us to consider
the effect of neutral drag on the turbulent cascade of energy. In a
collisionless plasma, neutral particle viscosity and ion-neutral drag will damp
mid-scale turbulent motions, but the power spectrum of the magnetic
perturbations extends below the viscous cutoff scale. We give a simple physical
picture of the magnetic field structure below this cutoff, consistent with
numerical experiments. We provide arguments for the reemergence of the
turbulent cascade well below the viscous cut-off scale and derive estimates for
field line diffusion on all scales. We note that this explains the persistence
of a single power law form for the turbulent power spectrum of the interstellar
medium, from scales of tens of parsecs down to thousands of kilometers. We find
that under typical conditions in the ISM stochastic reconnection speeds are
reduced by the presence of neutrals, but by no more than an order of magnitude.Comment: Astrophysical Journal in pres
Scatter broadening measurements of 124 pulsars at 327 MHz
We present the measurements of scatter broadening time-scales ()
for 124 pulsars at 327 MHz, using the upgraded Ooty Radio Telescope (ORT).
These pulsars lie in the dispersion measure range of 37 503 pc cm
and declination () range of 57. New
estimates for 58 pulsars are presented, increasing the sample of
all such measurements by about 40% at 327 MHz. Using all available
measurements in the literature, we investigate the dependence of on
dispersion measure. Our measurements, together with previously reported values
for , affirm that the ionized interstellar medium upto 3 kpc is
consistent with Kolmogorov spectrum, while it deviates significantly beyond
this distance.Comment: 19 pages, 4 figures, accepted for publication in Ap
Capabilities of Earth-based radar facilities for near-Earth asteroid observations
We evaluated the planetary radar capabilities at Arecibo, the Goldstone 70-m
DSS-14 and 34-m DSS-13 antennas, the 70-m DSS-43 antenna at Canberra, the Green
Bank Telescope, and the Parkes Radio Telescope in terms of their relative
sensitivities and the number of known near-Earth asteroids (NEAs) detectable
per year in monostatic and bistatic configurations. In the 2015 calendar year,
monostatic observations with Arecibo and DSS-14 were capable of detecting 253
and 131 NEAs respectively, with signal-to-noise ratios (SNRs) greater than
30/track. Combined, the two observatories were capable of detecting 276 NEAs.
Of these, Arecibo detected 77 and Goldstone detected 32, or 30% and 24% the
numbers that were possible. The two observatories detected an additional 18 and
7 NEAs respectively, with SNRs of less than 30/track. This indicates that a
substantial number of potential targets are not being observed. The bistatic
configuration with DSS-14 transmitting and the Green Bank Telescope receiving
was capable of detecting about 195 NEAs, or ~50% more than with monostatic
observations at DSS-14. Most of the detectable asteroids were targets of
opportunity that were discovered less than 15 days before the end of their
observing windows. About 50% of the detectable asteroids have absolute
magnitudes > 25, which corresponds diameters < ~30 m.Comment: 12 pages, 7 figures, Accepted to A
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