Spacetime Singularities in String and its Low Dimensional Effective Theory

Spacetime singularities are studied in both the $D+d$-dimensional string theory and its $D$-dimensional effective theory, obtained by the Kaluza-Klein compactification. It is found that spacetime singularities in the low dimensional effective theory may or may not remain after lifted to the $D+d$-dimensional string theory, depending on particular solutions. It is also found that there exist cases in which spacetime singularities appearing in high/low dimensional spacetimes do not necessarily happen on the same surfaces.Comment: revtex4, 15 pages, 10 figures. Typos are corrected. Version to appear in Inter. J. Mod. Phys.

Preliminary study on comparative morphometry of Cynothrissa mento (Regan, 1917) from Ologe, Badagry and Epe Lagoons, Lagos, Nigeria

The morphometric characters of Cynothrissa mento from three major Lagoons (Ologe, Badagry and Epe) in Lagos, Nigeria were compared to assess the possibility of this fish species from the three Lagoons belonging to the same sub-population. The length-weight relationships (LWR), and condition factors (CF) of the fish were also described as well as the physico-chemical parameters of the three water bodies. The study was conducted between May, 2009 and April, 2010 and monthly sampling of fish and water was done in each sampling site. Seven7 physico-chemical parameters were assessed and these are; temperature, pH, salinity, turbidity, dissolved oxygen, total alkalinity and total hardness. A total of 294 specimens (Ologe 60, Badagry 174 and Epe 60) of C. mento were collected from the landings of the local fisher folks from the sampling sites. Seven morphometric characters; total length (TL), standard length (SL), body depth (BD), head length (HL), head depth (HD), eye diameter (ED) and interorbital width (IW) were measured. There was no significant difference (p > 0.05) in all the physico-chemical parameters measured among the sampling sites except pH. Coefficient of difference revealed that the C. mento from the three lagoons are uniform in all the morphometric parameters examined, which means that the specimens from the three sampling sites do not belong to different sub-populations. The growth coefficient/slope (b) values obtained for the fish species from the sampling sites ranged from 2.27 - 2.53, and differed significantly (p < 0.05) from 3, which indicates that most of the fish species have negative algometric growth

Stability of spin-0 graviton and strong coupling in Horava-Lifshitz theory of gravity

In this paper, we consider two different issues, stability and strong coupling, raised lately in the newly-proposed Horava-Lifshitz (HL) theory of quantum gravity with projectability condition. We find that all the scalar modes are stable in the de Sitter background, due to two different kinds of effects, one from high-order derivatives of the spacetime curvature, and the other from the exponential expansion of the de Sitter space. Combining these effects properly, one can make the instability found in the Minkowski background never appear even for small-scale modes, provided that the IR limit is sufficiently closed to the relativistic fixed point. At the fixed point, all the modes become stabilized. We also show that the instability of Minkowski spacetime can be cured by introducing mass to the spin-0 graviton. The strong coupling problem is investigated following the effective field theory approach, and found that it cannot be cured by the Blas-Pujolas-Sibiryakov mechanism, initially designed for the case without projectability condition, but might be circumvented by the Vainshtein mechanism, due to the non-linear effects. In fact, we construct a class of exact solutions, and show explicitly that it reduces smoothly to the de Sitter spacetime in the relativistic limit.Comment: Some points regarding to strong coupling are further clarified, and typos corrected. revtex4, 9 figures. Version to appear in Physical Reviews

The Feasibility of R-Mode to Meet Resilient PNT Requirements for e-Navigation

Position, Navigation, and Timing (PNT) is part of the critical infrastructure necessary for the safety and efficient of vessel movements, especially in congested areas such as the North Sea. GNSS (primarily GPS and GLONASS) has become the primary PNT source for maritime operations. The GNSS position is used both for vessel navigation and as the position source for AIS. Unfortunately, GNSS is vulnerable to jamming and interference – not intentional and unintentional. This can lead to the loss of positioning information or even worse, to incorrect positioning information. The user requirement is for dependable PNT information at all times, even under GNSS jamming conditions. One potential source of resilient PNT services is Ranging Mode (R-Mode) using signals independent of GNSS. The German Federal Waterways and Shipping Administration has contracted for a feasibility study of R-mode using MF-DGNSS and VHF AIS signals as well as those signals in combination and in combination with eLoran. The first part of the study focused on the feasibility of using MF-DGNSS signals for ranging and timing. It examined the state of the art, identified potential solution methods, and, after examining Pros and Cons of the various options, selected a few options for further study. Part 2 examined the proposed solutions in depth and identified the modifications required for both the reference stations (transmitters) and user equipment (beacon receivers). Part 3 and 4 of the study repeated Parts 1 and 2, but using AIS signals rather than MF. Part 4 of the study examined the possibility of combining MF and AIS R-mode or combining MF R-Mode and eLoran. This paper presents the results of this study including recommended R-Mode implementations and bounds on the positioning performance using the various R-Mode methods. Included are predictions of DGNSS and AIS R-Mode coverage and the resulting HDOP using existing and preposed DGNSS and AUS sites with specific detail in the area of the planned test bed in the North Sea

A geometrical model of softwood anatomy for fluid mechanics simulations

This paper demonstrates a model of softwood geometry that can be used for multiscale modelling of the longitudinal movement of water through spruce wood. Previous results obtained from a high resolution X-ray CT scan and subsequent image analysis of a large number of Norway spruce tracheids were here used to produce a model that can represent the variability in wood anatomy found within a timber joist or log. A demonstration of that model is given

Tri-μ-oxido-bis­[(5,10,15,20-tetra­phenyl­porphyrinato-κ4 N)niobium(V)]

In the title dinuclear NbV compound, [Nb2(C44H28N4)2O3], each Nb atom is seven-coordinated with three bridging O atoms and four N atoms from a chelating tetra­phenyl­porphyrinate anion. The Nb—O bond lengths range from 1.757 (6) to 2.331 (6) Å, and the average (niobium–pyrrole N atom) distance is 2.239 Å. In the dinuclear mol­ecule, the Nb⋯Nb separation is 2.8200 (8) Å, and the dihedral angle between the two porphyrinate mean planes is 5.4 (1)°. Weak inter­molecular C—H⋯π inter­actions are present in the crystal structure

Relationships between Lower-body Power, Sprint and Change of Direction Speed among Collegiate Basketball Players by Sex

International Journal of Exercise Science 15(6): 974-984, 2022. The purpose of this study was to determine if significant relationships exist between absolute and relative lower-body power and selected measures of speed among male and female collegiate basketball players. Archived performance testing data from 29 (male = 14; female = 15) NCAA division II collegiate basketball players were used for this analysis. These measures included lane agility, 10-yard sprint, and shuttle run time (sec). A Pearson’s correlation coefficient was used to determine if significant relationships existed between measures of lower-body power and linear sprint time, change of direction speed (CODS), and shuttle performance. Statistical significance was set a priori at p ≤ 0.05. A significant large correlation was found between absolute power and lane agility (r = 0.54, p = 0.05) among male players. No significant correlations were found between absolute or relative power for 10-yard sprint times, lane agility, or shuttle run performance (p \u3e 0.05). Females showed no significant correlations between relative power and lane agility (r = -0.25, p = 0.37) or 10-yard sprint (r = -0.47, p = 0.08), but did show a significant large correlation (r = -0.64, p = 0.01) between relative power and shuttle run performance. Generating high amounts of relative power is vital in intermittent team sports such as basketball. In particular, this study provided evidence that relative power in female collegiate basketball players is significantly related to shuttle run ability

Levels of Analysis in Comprehensive River Basin Planning

Since nearly every water resource managment choice has two or more sides, differences must be resolved in decision making. Equitable resolution requires an understanding of the reasons for the differences. These reasons originate in the implemented plans have physical-environmental, economic, social, cultural, and political impacts at levels ranging from local to national or international in scope. Decisions are made by individuals and groups impacted in all of these dimensions and at all of these levels; the decisions generate additional impacts; and the entire interactive process changes water management practice in ways outside the control of any one decision point or even dicision dimension. The objective of this study is to conceptualize this process in a way that will help in establishing institutional mechanisms for reconciling differences among levels of analysis. The conceptualization used viewed differences in choices being made at the various levels of analysis as associated with perspective differences having value, jurisdiction, action, and temporal elements. The possible combinations of differences within and between these elements were used to identify ten categories of institutional obstacles to efficient water planning (differences in values, conflicts between value and jurisdiction, etc.). The history of water resources planning on the Colorado River basin was then examined to identify 17 specific institutional obstacles, and a computerized policy simulation was applied to levels of analysis in the Uintah basin of Utah to identify three more. These 20 obstacles were shown to be broadly distributed over the ten categories, and the nature of the obstacles defined provides valuable insight into the common characteristics of the major institutional obstacles to water management. The priciples of logic as applicable to rationality in decision making were then used to identify two root causes of levels\u27 conflicts. If alternatives are evaluated from a single perspective, the ostensible causal relationships commonly used lead to estimates of the sum of the consequences from the parts of a water management program being far more than the total consequences of the entire program. Looked at another way, since available water resources planning tools do not properly allocate consequences from interactive processes to individual causal sources, decisions made to acheive a desired impact are not based on reliable information. In fact, different decisions made over time from a single perspective have conflicting impacts. When multiple perspectices are considered, one finds that individual values do not aggregate linearly in forming social values, many actions are not efficient in achieving preferred values, and decision makers are not able to implement their plans as desired. Real world situations combine interacting perspectives and partial contributions. Nine recommendations are made on what to do next in improving water resources planning in an interactive, nonlinear world