Dynamics of the Australian summer monsoon

March 6, 1992.Includes bibliographical references.When a west-east line of deep convection forms over northern Australia, the potential vorticity field begins to change due to the latent heat release, with low level negative and upper level positive anomalies being induced. These potential vorticity patterns can be analytically derived by using a zonal balance model formulated in isentropic and potential latitude coordinates. The associated wind and mass fields can be found by solving an invertibility principle which is valid for these equatorial balanced flows. Since the convectively induced potential vorticity anomalies develop from an initial state which has potential vorticity increasing toward the north, reversed poleward gradients of potential vorticity are produced. The regions of potential vorticity gradient reversal are found on the poleward side of the ITCZ at low levels and on the equatorward side of the ITCZ at upper levels, just as in the observed fields during AMEX. For typical convective heating rates, significant potential vorticity gradient reversals occur quickly - on the order of a few days. This sets the stage for combined barotropic-baroclinic instability, the formation of tropical waves, and t he breakdown of the ITCZ. We can understand the barotropic aspects of this breakdown t rough a normal mode stability analysis of the nondivergent barotropic model with either a hyperbolic tangent shear layer basic state zonal wind or an idealized three region profile in which there is a central (ITCZ) region of anomalous absolute vorticity, surrounded by regions of undisturbed absolute vorticity. The latter model can be solved analytically, which allows direct interpretation of the breakdown in terms of the phase locking and growth of the counterpropagating vorticity anomalies (essentially Rossby waves) located on the two interfaces separating the three regions. In this sense the ITCZ is self-destructive and should not be viewed as a strictly steady state feature of the tropical circulation. In addition, according to this scenario, the potential vorticity dynamics of the Australian region are not unique, but are characterized by an ITCZ formation-breakdown cycle similar to that occurring in other tropical regions such as the tropical east Pacific and western Africa

Mapping the Galactic Halo. V. Sgr dSph Tidal Debris 60 degrees from the Main Body

As part of the Spaghetti Project Survey (SPS) we have detected a concentration of giant stars well above expectations for a smooth halo model. The position (l~350, b~50) and distance (~50 kpc) of this concentration match those of the Northern over-density detected by SDSS (Yanny et al. 2000, Ivezic et al. 2000). We find additional evidence for structure at ~80 kpc in the same direction. We present radial velocities for many of these stars, including the first published results from the 6.5m Magellan telescope. The radial velocities for stars in these structures are in excellent agreement with models of the dynamical evolution of the Sgr dwarf tidal debris, whose center is 60 degrees away. The metallicity of stars in these streams is lower than that of the main body of the Sgr dwarf, which may indicate a radial metallicity gradient prior to disruption.Comment: 10 pages, 3 figures accepted in Astrophysical Journal Letter

Mapping the Galactic Halo I. The `Spaghetti' Survey

We describe a major survey of the Milky Way halo designed to test for kinematic substructure caused by destruction of accreted satellites. We use the Washington photometric system to identify halo stars efficiently for spectroscopic followup. Tracers include halo giants (detectable out to more than 100 kpc), blue horizontal branch stars, halo stars near the main sequence turnoff, and the ``blue metal-poor stars'' of Preston et al (1994). We demonstrate the success of our survey by showing spectra of stars we have identified in all these categories, including giants as distant as 75 kpc. We discuss the problem of identifying the most distant halo giants. In particular, extremely metal-poor halo K dwarfs are present in approximately equal numbers to the distant giants for V fainter than 18, and we show that our method will distinguish reliably between these two groups of metal-poor stars. We plan to survey 100 square degrees at high galactic latitude, and expect to increase the numbers of known halo giants, BHB stars and turnoff stars by more than an order of magnitude. In addition to the strong test that this large sample will provide for the question `was the Milky Way halo accreted from satellite galaxies?', we will improve the accuracy of mass measurements of the Milky Way beyond 50 kpc via the kinematics of the many distant giants and BHB stars we will find. We show that one of our first datasets constrains the halo density law over galactocentric radii of 5-20 kpc and z heights of 2-15 kpc. The data support a flattened power-law halo with b/a of 0.6 and exponent -3.0. More complex models with a varying axial ratio may be needed with a larger dataset.Comment: 55 pages, 22 figures, to appear in the Astronomical Journa

The impact of helmets on motorcycle head trauma at a tertiary hospital in Jamaica

<p>Abstract</p> <p>Background</p> <p>Although the Jamaica road traffic act mandates motorcycle riders to wear approved helmets, opponents suggest that the local road conditions obviate any benefits from helmet use that have been proven in Developed countries. They suggest that the narrow, winding, poorly surfaced, congested local highways do not allow motorcyclists to sustain high velocity travel. The accidents then tend to occur at lower speeds and are accompanied by less severe injuries. This study was carried out to determine the impact of helmet use on traumatic brain injuries from motorcycle collisions in patients admitted to a tertiary referral hospital in Jamaica.</p> <p>Methods</p> <p>A prospectively collected trauma registry maintained by the Department of Surgery at the University Hospital of the West Indies in Jamaica was accessed to identify all motorcycle collision victims from January 2000 to January 2007. The therapeutic outcomes of traumatic brain injuries were compared between helmeted and un-helmeted riders. The data was analyzed using SPSS Version 12.</p> <p>Results</p> <p>Of 293 motorcycle collision victims, 143 sustained brain injuries. There were 9 females (6.3%) with an average age of 23 +/- 7.3 years and 134 males (93.7%) at an average age of 33.4 +/- 11.2 years (mean +/- SD). Only 49 (34.3%) patients wore a helmet at the time of a collision. Helmet use at the time of a collision significantly reduced the severity of head injuries (28.6% vs 46.8%, P = 0.028) and the likelihood of sustaining intra-cranial lesions (26.5% vs 44.7%, P = 0.03) from head injuries.</p> <p>Conclusion</p> <p>Wearing a helmet at the time of a motorcycle collision reduces the severity of head injuries. However, the prevalence of helmet use at the time of a collision is unacceptably low.</p

The radial velocity dispersion profile of the Galactic halo: constraining the density profile of the dark halo of the Milky Way

We have compiled a new sample of 240 halo objects with accurate distance and radial velocity measurements, including globular clusters, satellite galaxies, field blue horizontal branch (FHB) stars and red giant stars from the Spaghetti survey. The new data lead to a significant increase in the number of known objects for Galactocentric radii beyond 50 kpc, which allows a reliable determination of the radial velocity dispersion profile out to very large distances. The radial velocity dispersion shows an almost constant value of 120 km s −1 out to 30 kpc and then continuously declines down to 50 km s −1 at about 120 kpc. This fall-off puts important constraints on the density profile and total mass of the dark matter halo of the Milky Way. For a constant velocity anisotropy, the isothermal profile is ruled out, while both a dark halo following a truncated flat (TF) model of mass 1.2 +1.8 −0.5 × 10 12  M ⊙ and a Navarro, Frenk & White (NFW) profile of mass 0.8 +1.2 −0.2 × 10 12  M ⊙ and c = 18 are consistent with the data. The significant increase in the number of tracers combined with the large extent of the region probed by these has allowed a more precise determination of the Milky Way mass in comparison to previous works. We also show how different assumptions for the velocity anisotropy affect the performance of the mass models.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73086/1/j.1365-2966.2005.09367.x.pd

Measuring Five Dimensions of Religiosity Across Adolescence

This paper theorizes and tests a latent variable model of adolescent religiosity in which five dimensions of religiosity are interrelated: religious beliefs, religious exclusivity, external religiosity, private practice, and religious salience. Research often theorizes overlapping and independent influences of single items or dimensions of religiosity on outcomes such as adolescent sexual behavior, but rarely operationalizes the dimensions in a measurement model accounting for their associations with each other and across time. We use longitudinal structural equation modeling (SEM) with latent variables to analyze data from two waves of the National Study of Youth and Religion. We test our hypothesized measurement model as compared to four alternate measurement models and find that our proposed model maintains superior fit. We then discuss the associations between the five dimensions of religiosity we measure and how these change over time. Our findings suggest how future research might better operationalize multiple dimensions of religiosity in studies of the influence of religion in adolescence

Surviving Endoplasmic Reticulum Stress Is Coupled to Altered Chondrocyte Differentiation and Function

In protein folding and secretion disorders, activation of endoplasmic reticulum (ER) stress signaling (ERSS) protects cells, alleviating stress that would otherwise trigger apoptosis. Whether the stress-surviving cells resume normal function is not known. We studied the in vivo impact of ER stress in terminally differentiating hypertrophic chondrocytes (HCs) during endochondral bone formation. In transgenic mice expressing mutant collagen X as a consequence of a 13-base pair deletion in Col10a1 (13del), misfolded α1(X) chains accumulate in HCs and elicit ERSS. Histological and gene expression analyses showed that these chondrocytes survived ER stress, but terminal differentiation is interrupted, and endochondral bone formation is delayed, producing a chondrodysplasia phenotype. This altered differentiation involves cell-cycle re-entry, the re-expression of genes characteristic of a prehypertrophic-like state, and is cell-autonomous. Concomitantly, expression of Col10a1 and 13del mRNAs are reduced, and ER stress is alleviated. ERSS, abnormal chondrocyte differentiation, and altered growth plate architecture also occur in mice expressing mutant collagen II and aggrecan. Alteration of the differentiation program in chondrocytes expressing unfolded or misfolded proteins may be part of an adaptive response that facilitates survival and recovery from the ensuing ER stress. However, the altered differentiation disrupts the highly coordinated events of endochondral ossification culminating in chondrodysplasia