Graphs with the strong Havel-Hakimi property

The Havel-Hakimi algorithm iteratively reduces the degree sequence of a graph to a list of zeroes. As shown by Favaron, Mah\'eo, and Sacl\'e, the number of zeroes produced, known as the residue, is a lower bound on the independence number of the graph. We say that a graph has the strong Havel-Hakimi property if in each of its induced subgraphs, deleting any vertex of maximum degree reduces the degree sequence in the same way that the Havel-Hakimi algorithm does. We characterize graphs having this property (which include all threshold and matrogenic graphs) in terms of minimal forbidden induced subgraphs. We further show that for these graphs the residue equals the independence number, and a natural greedy algorithm always produces a maximum independent set.Comment: 7 pages, 3 figure

Inextendibility of spacetimes and Lorentzian length spaces

We study the low-regularity (in-)extendibility of spacetimes within the synthetic-geometric framework of Lorentzian length spaces developed in [KS:17]. To this end, we introduce appropriate notions of geodesics and timelike geodesic completeness and prove a general inextendibility result. Our results shed new light on recent analytic work in this direction and, for the first time, relate low-regularity inextendibility to (synthetic) curvature blow-up.Comment: 21 pages, 1 figure, made assumptions in 5.4 and 5.6 more explicit (strong causality and local TL geodesic connectedness of extension

THE SPECIAL SAFEGUARD MECHANISM IN THE DOHA DEVELOPMENT AGENDA: A CASE STUDY OF SOYBEANS

The Special Safeguard Mechanism (SSM) proposed for developing countries has become a thorny issue in the Doha Development Agenda’s (DDA) agricultural negotiations. Proponents of the mechanism argue that it is a necessary compromise to counter sharp price declines or rapid import surges in staple commodity markets of developing nations. Opponents of the SSM, which include many developed exporters, contend that the policy flexibility contained in current SSM proposals would severely limit market access if the mechanism is triggered. The impact of the SSM depends on a number of parameters: the number of times the SSM is triggered, whether the price or volume SSM is triggered, the size of current tariffs, the magnitude with which tariffs are reduced in the DDA, and the number of times a developing country will actually make use of the SSM. This study introduces a static, synthetic, global, partial equilibrium model of the world soybean complex to assess the preliminary aspects of the DDA’s proposed tariff cuts. Future work on this project will extend the model to a stochastic framework from which to simulate the effects of an SSM combined with the DDA tariff cutting formulas for developing nations.Agribusiness,

The Hawking-Penrose singularity theorem for C1,1C^{1,1}-Lorentzian metrics

We show that the Hawking--Penrose singularity theorem, and the generalisation of this theorem due to Galloway and Senovilla, continue to hold for Lorentzian metrics that are of $C^{1, 1}$-regularity. We formulate appropriate weak versions of the strong energy condition and genericity condition for $C^{1,1}$-metrics, and of $C^0$-trapped submanifolds. By regularisation, we show that, under these weak conditions, causal geodesics necessarily become non-maximising. This requires a detailed analysis of the matrix Riccati equation for the approximating metrics, which may be of independent interest.Comment: Minor amendments in v4: Removed non-equivalent condition from Def. 2.2 and adapted Lemma 3.5 and the proof of Lemma 3.

Natural Killer Cell Function and Dysfunction in Hepatitis C Virus Infection

Viruses must continually adapt against dynamic innate and adaptive responses of the host immune system to establish chronic infection. Only a small minority (∼20%) of those exposed to hepatitis C virus (HCV) spontaneously clear infection, leaving approximately 200 million people worldwide chronically infected with HCV. A number of recent research studies suggest that establishment andmaintenance of chronicHCVinfection involve natural killer (NK) cell dysfunction. This relationship is illustrated in vitro by disruption of typicalNK cell responses including both cell-mediated cytotoxicity and cytokine production. Expression of a number of activating NK cell receptors in vivo is also affected in chronic HCV infection.Thus, direct in vivo and in vitro evidence of compromised NK function in chronic HCV infection in conjunction with significant epidemiological associations between the outcome of HCV infection and certain combinations of NK cell regulatory receptor and class I human histocompatibility linked antigen (HLA) genotypes indicate that NK cells are important in the immune response against HCV infection. In this review, we highlight evidence suggesting that selective impairment of NK cell activity is related to establishment of chronic HCV infection

Testing of Noodle Creek Site 41JS102 Jones County, Texas

Staff Archeologists from the Environmental Affairs Division of Texas Department of Transportation discovered buried cultural resources that constitute archeological site 41JS102, in June and July 2001 at the proposed location of a bridge replacement over Noodle Creek in Jones County, Texas. Shovel testing and backhoe trenching revealed cultural material at 65 cm below the surface. Following this discovery the Texas Department of Transportation made recommendations to the Texas Historical Commission to assess site 41JS 102 and they concurred. In September 2001 archeologists from the Texas Department of Transportation initiated the site assessment phase. Landowner complications halted that work before completion. Subsequently, TRC Environmental was provided a Work Authorization under an existing general services contract to complete the assessment of 41JS102 in December 2001. The fieldwork consisted of the hand excavation and documentation of eight 1 by 1 m test units and the digging and documenting of six backhoe trenches. Limited and scattered historic artifacts were recovered from the upper parts of the two alluvial terraces (T0 and T1). A prehistoric component with quantities of lithic debitage and sparse burned rocks, limited stone tools and mussel shells, and one possible cultural feature were encountered in a sloping, but well defined 10 to 15 cm thick zone in the T1 deposits. The Principal Investigator recommended prehistoric site 4 1JS102 was eligible for inclusion in the National Register of Historic Places and as a State Archeological Landmark. However, the staff at Texas Department of Transportation disagreed with that recommendation and presented an opposing case to the Texas Historical Commission who concurred with the Texas Department of Transportation\u27s recommendations. Consequently, no further archeological investigations will occur prior to the proposed development

The Varga Site: A Multicomponent, Stratified Campsite in the Canyonlands of Edwards County, Texas

Data recovery excavations at the Varga Site were conducted in two phases during 2002 by archeologists from the Cultural Resources Department of TRC Environmental Corporation’s (TRC’s) Austin office under contract to Texas Department of Transportation (TxDOT) Scientific Service Contract No. 572XXSA004. This mitigation program was necessitated by the proposed reconstruction of the crossing of a Ranch to Market Road over Hackberry Creek, immediately south of the site in northeastern Edwards County. These archeological investigations were conducted as part of the responsibilities of TxDOT under existing federal and state legislation for the protection of cultural resources. Geoarcheological trenching and hand-excavations within the existing 31 m wide road right-of-way of 7- m-wide paved Ranch to Market Road focused on the alluvial fines in the first terrace overlooking Hackberry Creek immediately adjacent to a spring. The southern edge of the terrace contains relatively fine-grained sediments ranging from 15 to 150 centimeter (cm) thick that overlie coarse stream gravels that extend to an unknown depth. The modern ground surface had been impacted by road construction and maintenance activities, as well as by light erosion. Block Excavations were conducted on both sides of the pavement and resulted in the hand-excavations of a total of 207.75 square meters (m2), including 83 m2 (66.2 m3) in Block A on the western side and a 124.75 m2 (38.26 m3) area in Block B on the eastern side. Archeological deposits in the investigated part of the site extend to the southern lip of the first terrace and extend about 50 m to the north. The excavations yielded evidence of a multiple component campsite with three distinct and a fourth less distinct prehistoric components. In Block A, the 100 to 150 cm thick fine-grained sediments yielded four intact cultural components. Block B only targeted the youngest, Toyah component. The fine-grained alluvial sediments that comprise the first terrace contain discrete occupations radiocarbon dated to the Late Prehistoric period Toyah phase (ca. 290 to 660 B.P.), the Late Archaic period (ca. 1,700 to 2,300 B.P.), and the Early Archaic period (ca. 5,200 to 6,300 B.P.). A Middle Archaic period (ca. 3,900 to 4,800 B.P.) component was also recognized, but was not as clearly defined as were the other three components. Krotovina disturbance was relatively extensive in parts of the investigated site area. Nevertheless, the archeological deposits exhibited a high degree of contextual integrity. The Toyah phase component contains a rich assemblage of cultural material (ca. 65,000 pieces), including lithic debitage (ca. 26,000), quantities of highly fragmented bones (ca. 18,700), small burned rocks (ca. 16,000), formal and informal stone tools (ca. 1,850), scattered ceramic sherds (ca. 100), and 11 burned rock features. This component was radiocarbon dated by 14 accepted dates to between 290 and 660 B.P. Preservation was generally good, but mixing and probable overprinting contributed to poor horizontal patterning and an inability to identify discrete activity areas. The Late Archaic period component consists primarily of a large, nearly 6 m diameter lens of burned rock that is interpreted as an incipient burned rock midden with an indistinct central pit oven. This feature was associated with a buried A horizon and exhibited a high degree of stratigraphic integrity. However, beyond the ill-defined boundaries of this burned rock feature, limited lithic debitage assemblage (ca. 1,800), a few mussel shell fragments, five isolated burned rock features, scattered burned rocks, and occasional chipped stone tools (ca. 30) totaling less than 6,000 pieces. Identified dart point styles associated with this midden include Frio, Marcos, Ensor, Castroville, and Edgewood. This component was radiocarbon dated by 11 accepted dates to a 600-year period between 1,700 and 2,310 B.P. The Middle Archaic component was not well-defined, but definitely present and dispersed below the Late Archaic component and above the Early Archaic component. These materials were vertically distributed over a 20 to 40 cm thick zone that lacked completely sterile levels or visible breaks in the stratigraphy between the other cultural events. Lithic debitage (ca. 4,400) dominates the recovered assemblage (ca. 6,000), with limited burned rocks (ca. 3,000), a few formal chipped stone tools (ca. 25), and moderate frequency of vertebrate remains (100 g) also present. Two poorly organized burned rock features were also identified and documented. Five Early Triangular projectile points and one Carrizo point fragment occurred within this component. Two wood charcoal assays and one radiocarbon date on a deer bone directly date this Middle Archaic component to ca. 900-radiocarbon year period between 3,910 and 4,820 B.P. These three absolute dates are stratigraphically in order compared to the radiocarbon dates from the cultural components above and below. The Early Archaic component was defined by quantities of dense cultural debris (ca. 135,000) within a roughly 30 cm thick zone directly on top and mixed into coarse river gravels and below the Middle Archaic component. The cultural material varied in depth from a shallow 50 cm below datum (bd) at the north end to a much deeper 120 cmbd in the southern end of Block A. The recovery of a robust assemblage of dart points (170 specimens) that consisted of Group 2—Early Corner-Notched, Bandy, Martindale, Gower, and Merrell dart points indicates that this zone represents many occupations that occurred over a relatively broad time frame. The dart points were associated with a diverse tool assemblage (ca. 1,300). Organic preservation was poor in this lower stratum, but occasional fragments of animal bone, plant seeds, and wood charcoal were recovered. Fifteen organic samples of diverse materials yielded radiocarbon dates that document a minimum use period of 1,080-radiocarbon years from 5,200 B.P. to 6,280 B.P. Greater insight and understanding of each of these four components represented was made possible through the employment of numerous technical analyses, including the radiocarbon dating of 66 samples, six optically stimulated luminescence dates, use-wear analysis and organic residue identifications on 156 stone specimens, petrographic analyses on 18 pottery and one local sediment samples, pollen and phytolith analyses on 25 paired samples, instrumental neutron activation analysis on 261 chert samples and 18 pottery sherds, fatty acid composition on eight pottery sherds and 94 burned rocks, stable carbon and nitrogen analyses on 112 samples, macrobotanical analyses on 44 float and 75 individual charcoal samples, and granulometric and compositional studies on 10 sediment samples. The combined results have contributed significantly to a greater understanding of the Varga Site as a whole and documented specific information concerning the behaviors of the people who occupied the site. These and other technical analyses are urged for other excavated sites in the future to continue to broaden our understanding of the human behaviors at specific sites and throughout the broader region. This will add to a growing database that will foster a better understanding of prehistoric lifeways across Texas

A Thirty Kiloparsec Chain of "Beads on a String" Star Formation Between Two Merging Early Type Galaxies in the Core of a Strong-Lensing Galaxy Cluster

New Hubble Space Telescope ultraviolet and optical imaging of the strong-lensing galaxy cluster SDSS J1531+3414 (z=0.335) reveals two centrally dominant elliptical galaxies participating in an ongoing major merger. The interaction is at least somewhat rich in cool gas, as the merger is associated with a complex network of nineteen massive superclusters of young stars (or small tidal dwarf galaxies) separated by ~1 kpc in projection from one another, combining to an estimated total star formation rate of ~5 solar masses per year. The resolved young stellar superclusters are threaded by narrow H-alpha, [O II], and blue excess filaments arranged in a network spanning ~27 kpc across the two merging galaxies. This morphology is strongly reminiscent of the well-known "beads on a string" mode of star formation observed on kpc-scales in the arms of spiral galaxies, resonance rings, and in tidal tails between interacting galaxies. Nevertheless, the arrangement of this star formation relative to the nuclei of the two galaxies is difficult to interpret in a dynamical sense, as no known "beads on a string" systems associated with kpc-scale tidal interactions exhibit such lopsided morphology relative to the merger participants. In this Letter we present the images and follow-up spectroscopy, and discuss possible physical interpretations for the unique arrangement of the young stellar clusters. While we suggest that this morphology is likely to be dynamically short-lived, a more quantitative understanding awaits necessary multiwavelength follow-up, including optical integral field spectroscopy, ALMA sub-mm interferometry, and Chandra X-ray imaging.Comment: 7 pages, 4 figures, accepted for publication in ApJ Letters. High resolution images of the cluster can be found at http://hubblesite.org/news/2014/2