The time resolved measurement of ultrashort THz-band electric fields without an ultrashort probe

The time-resolved detection of ultrashort pulsed THz-band electric field temporal profiles without an ultrashort laser probe is demonstrated. A non-linear interaction between a narrow-bandwidth optical probe and the THz pulse transposes the THz spectral intensity and phase information to the optical region, thereby generating an optical pulse whose temporal electric field envelope replicates the temporal profile of the real THz electric field. This optical envelope is characterised via an autocorrelation based FROG measurement, hence revealing the THz temporal profile. The combination of a narrow-bandwidth, long duration, optical probe and self-referenced FROG makes the technique inherently immune to timing jitter between the optical probe and THz pulse, and may find particular application where the THz field is not initially generated via ultrashort laser methods, such as the measurement of longitudinal electron bunch profiles in particle accelerators.Comment: 7 pages, 3 figures, submitted to AP

The Snedden-Farnsworth Exchanges of 1917 and 1918 on the Value of Music and Art in Education

In 1917 and 1918, Charles Hubert Farnsworth, a leading music educator from Teachers College, Columbia University, and David Snedden, a critic and educational theorist of national repute, privately exchanged views on the role of art and music in society and in education. Snedden mulled over Herbert Spencer's query “What knowledge is of most worth?” and concluded that music must have practical survival value: it must contribute primarily to the maintenance of social and political order and secondarily to other aims. Farnsworth, on the other hand, thought that music performance or appreciation should be for the immediate joy that it gives the individual, not for some deferred social purpose no matter how important it might be. These divergent positions are explained in light of Farnsworth's interests in philosophy and Snedden's schooling in Spencerian and Darwinian thought.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68979/2/10.2307_3345173.pd

A Search for Planetary Nebulae With the SDSS: the outer regions of M31

We have developed a method to identify planetary nebula (PN) candidates in imaging data of the Sloan Digital Sky Survey (SDSS). This method exploits the SDSS' five-band sampling of emission lines in PN spectra, which results in a color signature distinct from that of other sources. Selection criteria based on this signature can be applied to nearby galaxies in which PNe appear as point sources. We applied these criteria to the whole area of M31 as scanned by the SDSS, selecting 167 PN candidates that are located in the outer regions of M31. The spectra of 80 selected candidates were then observed with the 2.2m telescope at Calar Alto Observatory. These observations and cross-checks with literature data show that our method has a selection rate efficiency of about 90%, but the efficiency is different for the different groups of PNe candidates. In the outer regions of M31, PNe trace different well-known morphological features like the Northern Spur, the NGC205 Loop, the G1 Clump, etc. In general, the distribution of PNe in the outer region 8<R<20 kpc along the minor axis shows the "extended disk" - a rotationally supported low surface brightness structure with an exponential scale length of 3.21+/-0.14 kpc and a total mass of ~10^10 M_{\sun}, which is equivalent to the mass of M33. We report the discovery of three PN candidates with projected locations in the center of Andromeda NE, a very low surface brightness giant stellar structure in the outer halo of M31. Two of the PNe were spectroscopically confirmed as genuine PNe. These two PNe are located at projected distances along the major axis of ~48 Kpc and ~41 Kpc from the center of M31 and are the most distant PNe in M31 found up to now.Comment: 58 pages, 17 figures, 2 tables, Accepted to Astronomical Journa

Application of fluvial scaling relationships to reconstruct drainage-basin evolution and sediment routing for the Cretaceous and Paleocene of the Gulf of Mexico

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.Fluvial systems represent a key component in source-to-sink analysis of ancient sediment-dispersal systems. Modern river channels and channel-related deposits possess a range of scaling relationships that reflect drainage-basin controls on water and sediment flux. For example, channel-belt sand-body thicknesses scale to bankfull discharge, and represent a reliable first-order proxy for contributing drainage-basin area, a proxy that is more robust if climatic regimes can be independently constrained. A database of morphometrics from Quaternary channel belts provides key modern fluvial system scaling relationships, which are applied to Cretaceous- to Paleocene-age fluvial deposits. This study documents the scales of channel-belt sand bodies within fluvial successions from the northern Gulf of Mexico passive-margin basin fill from well logs, and uses scaling relationships developed from modern systems to reconstruct the scale of associated sediment-routing systems and changes in scale through time. We measured thicknesses of 986 channel-belt sand bodies from 248 well logs so as to estimate the scales of the Cretaceous (Cenomanian) Tuscaloosa-Woodbine, Paleocene–early Eocene Wilcox, and Oligocene Vicksburg-Frio fluvial systems. These data indicate that Cenozoic fluvial systems were significantly larger than their Cenomanian counterparts, which is consistent with Cretaceous to Paleocene continental-scale drainage reorganization that routed water discharge and sediment from much of the continental United States to the Gulf of Mexico. At a more detailed level, Paleocene–early Eocene Wilcox fluvial systems were larger than their Oligocene counterparts, which could reflect decreases in drainage-basin size and/or climatic change within the continental interior toward drier climates with less runoff. Additionally, these data suggest that the paleo–Tennessee River, which now joins the Ohio River in the northernmost Mississippi embayment of the central United States, was an independent fluvial system, flowing southwest to the southern Mississippi embayment, or directly to the Gulf of Mexico, through the early Eocene. Changes in scaling relationships through time, and interpreted changes in the scales of contributing drainage basins, are generally consistent with previously published regional paleogeographic maps, as well as with newly published maps of paleodrainage from detrital-zircon provenance and geochronological studies. As part of a suite of metrics derived from modern systems, scaling relationships make it possible to more fully understand and constrain the scale of ancient source-to-sink systems and their changes through time, or cross-check interpretations made by other means

Channel-belt scaling relationship and application to early Miocene source-to-sink systems in the Gulf of Mexico basin

In past decades, numerous studies have focused on the alluvial sedimentary record of basin fill. Paleo–drainage basin characteristics, such as drainage area or axial river length, have received little attention, mostly because the paleo–drainage system underwent erosion or bypass, and its record is commonly modified and overprinted by subsequent tectonism or erosional processes. In this work, we estimate the drainage areas of early Miocene systems in the Gulf of Mexico basin by using scaling relationships between drainage area and river channel dimensions (e.g., depth) developed in source-to-sink studies. Channel-belt thickness was used to estimate channel depth and was measured from numerous geophysical well logs. Both lower channel-belt thickness and bankfull thickness were measured to estimate the paleo–water depth at low and bankfull stages. Previous paleogeographic reconstruction using detrital zircon and petrographic provenance analysis and continental geomorphic synthesis constrains independent estimates of drainage basin extent. Comparison of results generated by the two independent approaches indicates that drainage basin areas predicted from channel-belt thickness are reasonable and suggests that bankfull thickness correlates best with drainage basin area. The channel bankfull thickness also correlates with reconstructed submarine fan dimension. This work demonstrates application to the deep-time stratigraphic archive, where records of drainage basin characteristics are commonly modified or lost

Validation of empirical source-to-sink scaling relationships in a continental-scale system: The Gulf of Mexico basin Cenozoic record

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.Empirical scaling relationships between known deepwater siliciclastic submarine fan systems and their linked drainage basins have previously been established for modern to submodern depositional systems and in a few ancient, small-scale basins. Comprehensive mapping in the subsurface Gulf of Mexico basin and geological mapping of the North American drainage network facilitates a more rigorous test of scaling relationships in a continental-size system with multiple mountain source terranes, rivers, deltas, slopes, and abyssal plain fan systems formed over 65 m.y. of geologic time. An immense database of drilled wells and high-quality industry seismic data in this prolific hydrocarbon basin provide the independent measure of deepwater fan distribution and dimensions necessary to test source-to-sink system scaling relationships. Analysis of over 40 documented deepwater fan and apron systems in the Gulf of Mexico, ranging in age from Paleocene to Pleistocene, reveals that submarine-fan system scales vary predictably with catchment length and area. All fan system run-out lengths, as measured from shelf margin to mapped fan termination, fall in a range of 10%–50% of the drainage basin length, and most are comparable in scale to large (Mississippi River–scale) systems although some smaller fans are present (e.g., Oligocene Rio Bravo system). For larger systems such as those of the Paleocene Wilcox depositional episodes, fan run-out lengths generally fall in the range of 10%–25% of the longest river length. Submarine fan widths, mapped from both seismic reflection data and well control, appear to scale with fan run-out lengths, though with a lower correlation (R2 = 0.40) probably due to uncertainty in mapping fan width in some subsalt settings. Catchment area has a high correlation (R2 = 0.85) with river length, suggesting that fluvial discharge and sediment flux may be primary drivers of ancient fan size. Validation of these first-order source-to-sink scaling relationships provides a predictive tool in frontier basins with less data. Application to less-constrained early Eocene fan systems of the southern Gulf of Mexico demonstrates the utility for exploration as well as paleogeographic reconstructions of ancient drainage systems. This approach has considerable utility in estimating dimensions of known but poorly constrained submarine fans in the subsurface or exposed in outcrop

The Case for Optically-Thick High Velocity Broad Line Region Gas in Active Galactic Nuclei

A combined analysis of the profiles of the main broad quasar emission lines in both Hubble Space Telescope and optical spectra shows that while the profiles of the strong UV lines are quite similar, there is frequently a strong increase in the Ly-alpha/H-alpha ratio in the high-velocity gas. We show that the suggestion that the high velocity gas is optically-thin presents many problems. We show that the relative strengths of the high velocity wings arise naturally in an optically-thick BLR component. An optically-thick model successfully explains the equivalent widths of the lines, the Ly-alpha/H-alpha ratios and flatter Balmer decrements in the line wings, the strengths of CIII] and the lambda 1400 blend, and the strong variability of high-velocity, high-ionization lines (especially HeII and HeI).Comment: 34 pages in AASTeX, including 10 pages of figures. Submitted to Astrophysical Journa

Detrital-zircon records of Cenomanian, Paleocene, and Oligocene Gulf of Mexico drainage integration and sediment routing: Implications for scales of basin-floor fans

This paper uses detrital zircon (DZ) provenance and geochronological data to reconstruct paleodrainage areas and lengths for sediment-routing systems that fed the Cenomanian Tuscaloosa-Woodbine, Paleocene Wilcox, and Oligocene Vicksburg-Frio clastic wedges of the northern Gulf of Mexico (GoM) margin. During the Cenomanian, an ancestral Tennessee-Alabama River system with a distinctive Appalachian DZ signature was the largest system contributing water and sediment to the GoM, with a series of smaller systems draining the Ouachita Mountains and discharging sediment to the western GoM. By early Paleocene Wilcox deposition, drainage of the southern half of North America had reorganized such that GoM contributing areas stretched from the Western Cordillera to the Appalachians, and sediment was delivered to a primary depocenter in the northwestern GoM, the Rockdale depocenter fed by a paleo–Brazos-Colorado River system, as well as to the paleo–Mississippi River in southern Louisiana. By the Oligocene, the western drainage divide for the GoM had migrated east to the Laramide Rockies, with much of the Rockies now draining through the paleo–Red River and paleo–Arkansas River systems to join the paleo–Mississippi River in the southern Mississippi embayment. The paleo–Tennessee River had diverted to the north toward its present-day junction with the Ohio River by this time, thus becoming a tributary to the paleo-Mississippi within the northern Mississippi embayment. Hence, the paleo-Mississippi was the largest Oligocene system of the northern GoM margin. Drainage basin organization has had a profound impact on sediment delivery to the northern GoM margin. We use paleodrainage reconstructions to predict scales of associated basin-floor fans and test our predictions against measurements made from an extensive GoM database. We predict large fan systems for the Cenomanian paleo–Tennessee-Alabama, and especially for the two major depocenters of the early Paleocene paleo–Brazos-Colorado and late Paleocene–earliest Eocene paleo-Mississippi systems, and for the Oligocene paleo-Mississippi. With the notable exception of the Oligocene, measured fans reside within the range of our predictions, indicating that this approach can be exported to other basins that are less data rich

Tilted Pulse-Front Phase-matching in Three Dimensions:Overcoming The Cherenkov Angle Restrictions

We consider the non-linear generation of THz with tilted pulse-fronts in three dimensions and show that, contrary to the widely held expectations, coherent phase matching can be obtained for pulse-front tilt angles other the Cherenkov angle

Optically Selected BL Lacertae Candidates from the Sloan Digital Sky Survey Data Release Seven

We present a sample of 723 optically selected BL Lac candidates from the SDSS DR7 spectroscopic database encompassing 8250 deg^2 of sky; our sample constitutes one of the largest uniform BL Lac samples yet derived. Each BL Lac candidate has a high-quality SDSS spectrum from which we determine spectroscopic redshifts for ~60% of the objects. Redshift lower limits are estimated for the remaining objects utilizing the lack of host galaxy flux contamination in their optical spectra; we find that objects lacking spectroscopic redshifts are likely at systematically higher redshifts. Approximately 80% of our BL Lac candidates match to a radio source in FIRST/NVSS, and ~40% match to a ROSAT X-ray source. The homogeneous multiwavelength coverage allows subdivision of the sample into 637 radio-loud BL Lac candidates and 86 weak-featured radio-quiet objects. The radio-loud objects broadly support the standard paradigm unifying BL Lac objects with beamed radio galaxies. We propose that the majority of the radio-quiet objects may be lower-redshift (z<2.2) analogs to high-redshift weak line quasars (i.e., AGN with unusually anemic broad emission line regions). These would constitute the largest sample of such objects, being of similar size and complementary in redshift to the samples of high-redshift weak line quasars previously discovered by the SDSS. However, some fraction of the weak-featured radio-quiet objects may instead populate a rare and extreme radio-weak tail of the much larger radio-loud BL Lac population. Serendipitous discoveries of unusual white dwarfs, high-redshift weak line quasars, and broad absorption line quasars with extreme continuum dropoffs blueward of rest-frame 2800 Angstroms are also briefly described.Comment: 24 pages, 14 figures, 8 tables. Accepted for publication in A