A note on positive energy of topologically massive gravity

I review how "classical SUGRA" embeddability establishes positive energy E for D=3 topologically massive gravity (TMG), with or without a cosmological term, a procedure familiar from D=4 Einstein gravity (GR). It also provides explicit expressions for E. In contrast to GR, E is not manifestly positive, due to the peculiar two-term nature of TMG.Comment: 7 page

Black Hole Entropy, Marginal Stability and Mirror Symmetry

We consider the superconformal quantum mechanics associated to BPS black holes in type IIB Calabi-Yau compactifications. This quantum mechanics describes the dynamics of D-branes in the near-horizon attractor geometry of the black hole. In many cases, the black hole entropy can be found by counting the number of chiral primaries in this quantum mechanics. Both the attractor mechanism and notions of marginal stability play important roles in generating the large number of microstates required to explain this entropy. We compute the microscopic entropy explicitly in a few different cases, where the theory reduces to quantum mechanics on the moduli space of special Lagrangians. Under certain assumptions, the problem may be solved by implementing mirror symmetry as three T-dualities: this is essentially the mirror of a calculation by Gaiotto, Strominger and Yin. In some simple cases, the calculation may be done in greater generality without resorting to conjectures about mirror symmetry. For example, the K3xT^2 case may be studied precisely using the Fourier-Mukai transform

Effects of concurrent activation potentiation on countermovement jump performance

The purpose of this study was to assess the effects of concurrent activation potentiation (CAP) on countermovement jump (CMJ) performance. Twenty-four resistance trained males (mean ± SD, age 25 ± 4 years; body mass: 78.7 ± 10.3 kg) performed a CMJ on a force plate under four different conditions: a) a control condition where the CMJ was performed with hands on hips and lips pursed, thus preventing jaw or fist contraction from occurring, b) a jaw condition where the CMJ was performed with maximal contraction of the jaw, c) a fist condition where the CMJ was performed with maximal contraction of the fists, and d) a combined condition where the CMJ was performed with maximal contraction of both jaw and fists. Jump height (JH), peak force (PF), rate of force development (RFD) and time to peak force (TTPF) were calculated from the vertical force trace. There was no significant difference in PF (P = 0.88), TTPF (P = 0.96), JH (P = 0.45), or RFD (P = 0.06) between the four conditions. Effect size (ES) comparisons suggests a potential for the BOTH condition to augment both PF (2.4%; ES: 0.62) and RFD (9.9%; ES: 0.94) over NORM. It is concluded that CAP via singular and combined contractions has no significant impact on CMJ performance, however, substantial inter-individual variation in the response to CAP was observed and such techniques may therefore warrant consideration on an individual basis

Does a loaded warm-up influence jump asymmetry and badminton-specific change of direction performance?

Purpose: Previously, it has been shown that loaded warm-up (LWU) can improve change of direction speed (CODS) in professional badminton players. However, the effect of asymmetry on CODS in badminton players and the influence of LWU on asymmetry has not been examined. Methods: Twenty-one amateur badminton players (age: 29.5 ± 8.4; playing experience: 8.4 ± 4.2 years) completed two trials. In the first, they performed a control warm-up (CWU). In the second, they performed the same warm-up but with three exercises loaded with a weight vest (LWU). Following both warm-ups, players completed single leg jump (SLCMJ) and badminton-specific CODS tests. Results: No significant differences between CWU and LWU were observed for CODS, SLCMJ or SLCMJ asymmetry. However, small effect sizes suggested faster CODS (mean difference: -5%; d = -0.32) and lower asymmetries (mean difference: -3%; d = -0.39) following LWU. Five players (24%) experienced CODS improvements greater than the minimum detectable change whilst two (10%) responded negatively. Asymmetry was not correlated with CODS following CWU (ρ = 0.079; p = 0.733) but was negatively associated with CODS after LWU (ρ = -0.491; p = 0.035). Conclusion: LWU may prove a strategy to trial on an individual basis but generic recommendations should not be applied

Train the engine or the brakes? Influence of momentum on the change of direction deficit

Purpose: Currently, it is unclear which physical characteristics may underpin the change of direction deficit (COD-D). This investigation sought to determine if momentum, speed-, and jump-based measures may explain variance in COD-D. Methods: Seventeen males from a professional soccer academy (age: 16.76 ± 0.75 years; height: 1.80 ± 0.06 m; body mass: 72.38 ± 9.57 kg) performed 505 tests on both legs, a 40-m sprint and single leg countermovement and drop jumps. Results: Regression analyses did not reveal any significant predictors for COD-D on either leg. “Large” relationships were reported between COD-D and 505 time on both limbs (r = 0.65-0.69; p < 0.01) but COD-D was not associated with linear momentum, speed- or jump-based performances. When the cohort was median split by COD-D, effect sizes suggested that the sub-group with the smaller COD-D were 5% faster in the 505 test (d = -1.24; p < 0.001) but 4% slower over 0-10-m (d = 0.79; p = 0.33) and carried 11% less momentum (d = -0.81; p = 0.17). Conclusion: Individual variance in COD-D may not be explained by speed- and jump-based performance measures within academy soccer players. However, when grouping athletes by COD-D, faster athletes with greater momentum are likely to display a larger COD-D. It may therefore be prudent to recommend more eccentric-biased or technical focused COD training in such athletes and for coaches to view the change of direction action as a specific skill that may not be represented by performance time in a COD test

Determinants of club head speed in PGA professional golfers

Club head speed (CHS) has been significantly correlated to golf performance, but only in amateurs. The purpose of this study therefore, was to investigate the relationship between field-based measures of strength and power with CHS in PGA professional golfers, and further, determine differences between age groups. A correlation design was used to test relationships between squat jump (SJ), seated medicine ball throw (SMBT), rotational medicine ball throw (RMBT) and CHS. Twenty participants volunteered to take part in the study (age: 31.95 +/- 8.7 years, height: 182.75 +/- 6.88cm, mass: 90.47 +/- 15.6kg). Intraclass correlation coefficients reported high reliability for performance variables (r = 0.85-0.95). Significant correlations (p 30 (n = 10; 39.7 +/- 5.5 years). Correlations to CHS for 30 also had significant correlations to CHS in SMBT (r = 0.881) and SJ (r = 0.729), but also in RMBT (r = 0.642). The results of this study suggest that SJ and SMBT have the largest contribution to CHS in PGA professional golfers. When comparing age groups, it appears that younger golfers ( 30 years) utilise more upper body strength. Results suggest that strength based leg exercises and power based chest exercises may improve CHS in professional golfers

Lower extremity stiffness: considerations for testing, performance enhancement and injury risk

Force-deformation characteristics of the lower limb have been associated with athletic performance and may modulate the risk of injury. In-spite of these known associations, measurements of lower extremity stiffness are not commonly administered by strength and conditioning coaches. This review provides an overview of the available literature pertaining to the effects of lower extremity stiffness on physical performance and injury risk. Practical methods of monitoring and training stiffness are also discussed. The cumulative body of evidence indicates that increases in lower extremity stiffness are associated with heightened performance in athletic tasks such as hopping, jumping, throwing, endurance running, sprinting and changing direction. Relationships with injury are less conclusive as both excessive and insufficient limb stiffness have been postulated to increase risk. Thus, the ‘optimal’ level of stiffness appears to be dependent on the anthropometry, and physical capabilities of the athlete, in addition to sport-specific activity demands. Training interventions can positively enhance lower extremity stiffness, including isometric, eccentric and isotonic strength training and plyometrics. Complex training also appears to provide a potent stimulus and may be more effective than the use of singular training modes. For plyometric activities, it is recommended that coaches use a developmental sequence of exercises with increasing eccentric demand to provide an appropriate stimulus based on the training age and technical competency of the athlete

Acute and chronic effects of foam rolling vs eccentric exercise on ROM and force output of the plantar flexors

Foam rolling and eccentric exercise interventions have been demonstrated to improve range of motion (ROM). However, these two modalities have not been directly compared. Twenty-three academy soccer players (age: 18 ± 1; height: 1.74 ± 0.08 m; body mass: 69.3 ± 7.5 kg) were randomly allocated to either a foam rolling (FR) or eccentric exercise intervention designed to improve dorsiflexion ROM. Participants performed the intervention daily for a duration of four weeks. Measurements of dorsiflexion ROM, isometric plantar flexion torque and drop jump reactive strength index were taken at baseline (pre-intervention) and at three subsequent time-points (30-min post, 24-hours post and 4-weeks post). A significant time x group interaction effect was observed for dorsiflexion (P = 0.036), but not for torque or reactive strength index. For dorsiflexion, there was a significant increase in both acute (30-min; P < 0.001) and chronic (4-week; P < 0.001) ROM for the eccentric group, whilst FR exhibited only an acute improvement (P < 0.001). Eccentric training would appear a more efficacious modality than foam rolling for improving dorsiflexion ROM in elite academy soccer players

Simple de Sitter Solutions

We present a framework for de Sitter model building in type IIA string theory, illustrated with specific examples. We find metastable dS minima of the potential for moduli obtained from a compactification on a product of two Nil three-manifolds (which have negative scalar curvature) combined with orientifolds, branes, fractional Chern-Simons forms, and fluxes. As a discrete quantum number is taken large, the curvature, field strengths, inverse volume, and four dimensional string coupling become parametrically small, and the de Sitter Hubble scale can be tuned parametrically smaller than the scales of the moduli, KK, and winding mode masses. A subtle point in the construction is that although the curvature remains consistently weak, the circle fibers of the nilmanifolds become very small in this limit (though this is avoided in illustrative solutions at modest values of the parameters). In the simplest version of the construction, the heaviest moduli masses are parametrically of the same order as the lightest KK and winding masses. However, we provide a method for separating these marginally overlapping scales, and more generally the underlying supersymmetry of the model protects against large corrections to the low-energy moduli potential.Comment: 37 pages, harvmac big, 4 figures. v3: small correction