1,504 research outputs found
Wireless Bandwidth Aggregation for Internet Traffic
This MQP proposes a new method for bandwidth aggregation, utilize-able by the typical home network owner. The methods explained herein aggregate a network of coordinating routers within local WiFi communication range to achieve increased bandwidth at the application layer, over the HTTP protocol. Our protocol guarantees content delivery and reliability, as well as non-repudiation measures that hold each participant, rather then the group of routers, accountable for the content they download
The Natural Ontological Attitude from a Physicist's Perspective: Towards Quantum Realism
The debate between Arthur Fine and Alan Musgrave is well known amongst those involved in the scientific realism debate and centres upon two papers that are quite often found together in philosophy of science anthologies. Reading them like this gives the very strong impression the Musgrave is the victor which is the commonly held view. In this thesis, I wish to overturn this view by placing Fine's paper in context, namely as part of a larger work on the history and philosophy of quantum physics. Fine's book, The Shaky Game: Einstein, Realism and Quantum Theory, gives us good reason to believe that quantum physics significantly undermines the whole scientific realism debate, and as such, has strongly influenced Fine's development of the Natural Ontological Attitude, which is as Fine believes a middle ground between realism and anti-realism. The present thesis evaluates the Natural Ontological Attitude from a physicist's perspective and defends Fine against Musgrave's reply to the extent that it demonstrates that Musgrave would do well to read Fine's paper in context.
That said, just as Fine in his youth hoped that a quantum realist position will one day be found, so I also possess this aspiration; and so, despite my concluding that Fine is justified in holding to NOA, I argue furthermore that NOA is but a precursor to a potential quantum structural realist position. After showing that structural realism is worthy of consideration by using it to counter Fine's objections to scientific realism, I analyse the results of quantum physics in an attempt to understand what it can tell us about reality in the quantum realm. Eliminativist Ontic Structural Realism holds great promise as a quantum realism contender, and as such, it inspired the questions regarding individuality and reality that are discussed in the final main chapter. I thus resuscitate hope that the cause of the quantum realist is not yet lost
THE EVOLUTION OF ARMS AND ARMORS DURING THE CRUSADES
The Crusades were a major turning point in history which evoked a rapid evolution of arms and armors that persisted throughout the middle ages. The focus of this project is to outline the historical, technological, and geographical context that lead to such an evolution. The information we collect will be presented on a continually growing website developed by previous groups. A great helm will also be crafted, in a way that captures the style and spirit of the ancient craft of blacksmithing
Accounting for Cosmic Variance in Studies of Gravitationally-Lensed High-Redshift Galaxies in the Hubble Frontier Field Clusters
Strong gravitational lensing provides a powerful means for studying faint
galaxies in the distant universe. By magnifying the apparent brightness of
background sources, massive clusters enable the detection of galaxies fainter
than the usual sensitivity limit for blank fields. However, this gain in
effective sensitivity comes at the cost of a reduced survey volume and, in this
{\it Letter}, we demonstrate there is an associated increase in the cosmic
variance uncertainty. As an example, we show that the cosmic variance
uncertainty of the high redshift population viewed through the Hubble Space
Telescope Frontier Field cluster Abell 2744 increases from ~35% at redshift z~7
to >~65% at z~10. Previous studies of high redshift galaxies identified in the
Frontier Fields have underestimated the cosmic variance uncertainty that will
affect the ultimate constraints on both the faint end slope of the
high-redshift luminosity function and the cosmic star formation rate density,
key goals of the Frontier Field program.Comment: 5 pages, 3 figures. Version accepted by ApJ
Observation of intraseasonal oscillation of 64 day in the ionospheric sporadic E layers using Indian MST Radar, SABER / TIMED instrument and Ionosonde present at Gadanki(13.5 N,79.2 E)
15th MST Radar WorkshopSession M6: Middle atmosphere dynamics and structureMay 30 (Tue), Poster Sessio
New Constraints on Cosmic Reionization from the 2012 Hubble Ultra Deep Field Campaign
Understanding cosmic reionization requires the identification and
characterization of early sources of hydrogen-ionizing photons. The 2012 Hubble
Ultra Deep Field (UDF12) campaign has acquired the deepest infrared images with
the Wide Field Camera 3 aboard Hubble Space Telescope and, for the first time,
systematically explored the galaxy population deep into the era when cosmic
microwave background (CMB) data indicates reionization was underway. The UDF12
campaign thus provides the best constraints to date on the abundance,
luminosity distribution, and spectral properties of early star-forming
galaxies. We synthesize the new UDF12 results with the most recent constraints
from CMB observations to infer redshift-dependent ultraviolet (UV) luminosity
densities, reionization histories, and electron scattering optical depth
evolution consistent with the available data. Under reasonable assumptions
about the escape fraction of hydrogen ionizing photons and the intergalactic
medium clumping factor, we find that to fully reionize the universe by redshift
z~6 the population of star-forming galaxies at redshifts z~7-9 likely must
extend in luminosity below the UDF12 limits to absolute UV magnitudes of
M_UV\sim -13 or fainter. Moreover, low levels of star formation extending to
redshifts z~15-25, as suggested by the normal UV colors of z\simeq7-8 galaxies
and the smooth decline in abundance with redshift observed by UDF12 to
z\simeq10, are additionally likely required to reproduce the optical depth to
electron scattering inferred from CMB observations.Comment: Version accepted by ApJ (originally submitted Jan 5, 2013). The UDF12
website can be found at http://udf12.arizona.ed
The DAF-16 FOXO transcription factor regulates natc-1 to modulate stress resistance in Caenorhabditis elegans, linking insulin/IGF-1 signaling to protein N-terminal acetylation
The insulin/IGF-1 signaling pathway plays a critical role in stress resistance and longevity, but the mechanisms are not fully characterized. To identify genes that mediate stress resistance, we screened for C. elegans mutants that can tolerate high levels of dietary zinc. We identified natc-1, which encodes an evolutionarily conserved subunit of the N-terminal acetyltransferase C (NAT) complex. N-terminal acetylation is a widespread modification of eukaryotic proteins; however, relatively little is known about the biological functions of NATs. We demonstrated that loss-of-function mutations in natc-1 cause resistance to a broad-spectrum of physiologic stressors, including multiple metals, heat, and oxidation. The C. elegans FOXO transcription factor DAF-16 is a critical target of the insulin/IGF-1 signaling pathway that mediates stress resistance, and DAF-16 is predicted to directly bind the natc-1 promoter. To characterize the regulation of natc-1 by DAF-16 and the function of natc-1 in insulin/IGF-1 signaling, we analyzed molecular and genetic interactions with key components of the insulin/IGF-1 pathway. natc-1 mRNA levels were repressed by DAF-16 activity, indicating natc-1 is a physiological target of DAF-16. Genetic studies suggested that natc-1 functions downstream of daf-16 to mediate stress resistance and dauer formation. Based on these findings, we hypothesize that natc-1 is directly regulated by the DAF-16 transcription factor, and natc-1 is a physiologically significant effector of the insulin/IGF-1 signaling pathway that mediates stress resistance and dauer formation. These studies identify a novel biological function for natc-1 as a modulator of stress resistance and dauer formation and define a functionally significant downstream effector of the insulin/IGF-1 signaling pathway. Protein N-terminal acetylation mediated by the NatC complex may play an evolutionarily conserved role in regulating stress resistance
Keck Spectroscopy of 3<z<7 Faint Lyman Break Galaxies: The Importance of Nebular Emission in Understanding the Specific Star Formation Rate and Stellar Mass Density
The physical properties inferred from the SEDs of z>3 galaxies have been
influential in shaping our understanding of early galaxy formation and the role
galaxies may play in cosmic reionization. Of particular importance is the
stellar mass density at early times which represents the integral of earlier
star formation. An important puzzle arising from the measurements so far
reported is that the specific star formation rates (sSFR) evolve far less
rapidly than expected in most theoretical models. Yet the observations
underpinning these results remain very uncertain, owing in part to the possible
contamination of rest-optical broadband light from strong nebular emission
lines. To quantify the contribution of nebular emission to broad-band fluxes,
we investigate the SEDs of 92 spectroscopically-confirmed galaxies in the
redshift range 3.8<z<5.0 chosen because the H-alpha line lies within the
Spitzer/IRAC 3.6 um filter. We demonstrate that the 3.6 um flux is
systematically in excess of that expected from stellar continuum, which we
derive by fitting the SED with population synthesis models. No such excess is
seen in a control sample at 3.1<z<3.6 in which there is no nebular
contamination in the IRAC filters. From the distribution of our 3.6 um flux
excesses, we derive an H-alpha equivalent width (EW) distribution. The mean
rest-frame H-alpha EW we infer at 3.8<z<5.0 (270 A) indicates that nebular
emission contributes at least 30% of the 3.6 um flux. Via our
empirically-derived EW distribution we correct the available stellar mass
densities and show that the sSFR evolves more rapidly at z>4 than previously
thought, supporting up to a 5x increase between z~2 and 7. Such a trend is much
closer to theoretical expectations. Given our findings, we discuss the
prospects for verifying quantitatively the nebular emission line strengths
prior to the launch of the James Webb Space Telescope.Comment: 16 pages, 9 figures, submitted to Ap
Raman spectroscopy of laser irradiated titanium dioxide.
Raman spectroscopy is applied to investigate the effect of exposure to high power laser radiation on the crystalline phases of TiO2. Measurement of the changes in the Raman spectra of TiO2 with exposure to laser radiation was reported. This has proved to be a useful sensor in monitoring both the structure and the kinetics process of change in crystalline phases from anatase to rutile during exposure to laser irradiation
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