String Theory and Turbulence

We propose a string theory of turbulence that explains the Kolmogorov scaling in 3+1 dimensions and the Kraichnan and Kolmogorov scalings in 2+1 dimensions. This string theory of turbulence should be understood in light of the AdS/CFT dictionary. Our argument is crucially based on the use of Migdal's loop variables and the self-consistent solutions of Migdal's loop equations for turbulence. In particular, there is an area law for turbulence in 2+1 dimensions related to the Kraichnan scaling.Comment: LaTeX; 15 pages, two figures; v.2: slight changes to text, footnotes and references adde

Quantum Gravity and Turbulence

We apply recent advances in quantum gravity to the problem of turbulence. Adopting the AdS/CFT approach we propose a string theory of turbulence that explains the Kolmogorov scaling in 3+1 dimensions and the Kraichnan and Kolmogorov scalings in 2+1 dimensions. In the gravitational context, turbulence is intimately related to the properties of spacetime, or quantum, foam.Comment: 8 pages, LaTeX; Honorable Mention in the 2010 Gravity Research Foundation Essay Contes

Thermal Behavior of Hydroxymethylated Resorcinol (HMR)-Treated Maple Veneer

The objective of this research was to study the effect of hydroxymethylated resorcinol (HMR) treatment on the thermal and dynamic mechanical properties of maple veneer. The veneers were soaked in HMR solution for either 1, 15, or 30 min, and subsequently dried for either 1, 12, or 24 h at 20°C and 65% relative humidity. Dynamic mechanical thermal analysis (DMTA) tests were performed at a controlled heating rate of 5°C/min using a 3-point bending mode at an oscillatory frequency of 1Hz and an oscillating dynamic strain of 0.01%. Differential scanning calorimetry (DSC) was performed from -40 to 150°C at a heating rate of 10°C/min. Depending on the amount of drying, the storage moduli of wood can be unaltered or reduced as a response to HMR soaking time. Overall, there was no evidence that HMR treatments reinforce wood.The lignin glass-transition temperature of HMR-treated maple veneer decreased with an increase in treatment time. The lowering of Tg by HMR treatments was confirmed by DSC results. Both DMTA and DSC data showed a glass-transition shift of wood hemicellulose that was subtle or none in responding to HMR treatments. HMR was theoretically determined to have a closer solubility parameter match (better compatibility) with lignin compared to the other wood cell-wall polymers (i.e., cellulose and hemicellulose). Based on these findings, HMR is postulated to act as a lignin plasticizer.This study provides new insights into the interactions of HMR with wood and is expected to stimulate further investigations that lead to a better understanding of the wood bond durability enhancement of HMR treatment

Influence of Stitch Density and Stitch Thread Thickness on Compression After Impact Strength of Stitched Composites

This study aims to investigate the influence of stitch density and stitch thread thickness on compression after impact (CAI) strength of stitched composites. Unstitched laminated composites and specimens stitched with varying stitch density and stitch thread thickness are subjected to impact damage and then compressive loading. It is shown that stitched composites have higher CAI strength than unstitched counterpart due to smaller impact-induced delamination area, where local buckling occurs during compressive failure. However, it is revealed that the effectiveness of stitching in suppressing delamination growth and inhibiting sublaminate buckling under compressive loading is intimately related to stitch density. It is also found out that stitch thread thickness has little influence on CAI strength at low impact energy level, but has considerable effect at high impact energy level

The Effect of Cyclic Relative Humidity Changes on Moisture Content and Thickness Swelling Behavior of Oriented Strandboard

This study examines the effect of cyclic RH exposure on MC and thickness swelling (TS) of oriented strandboard (OSB) made from fire-impacted trees. Two specimens were cut from the center of each OSB panel and one was edge-sealed. After being conditioned to 65% RH, specimens were placed in a climate-controlled chamber and subjected to three cyclic changes of 90 - 30% RH at 20°C. Experimental data were characterized by three time-dependent MC or TS models: logarithmic, power law, and exponential. The latter two models gave the best fits showing that edge-sealing reduced the extent of swelling during adsorption and reduced the moisture loss at desorption. The models also described the effect of burnt level and bark throughout the humidity exposure cycles. The exponential model revealed no significant effect of burnt level on the panel TS. Both the power law and exponential models indicated that addition of charred bark to the panels significantly decreased the maximum amount of moisture and thickness change. The exponential model revealed an increase in equilibrium TS at the end of each RH cycle compared with the end of precyclic desorption. True nonrecoverable TS was difficult to discern in Cycle 1 because of moisture hysteresis, but the nonrecoverable effect was evident in Cycles 2 and 3

Validation of Delamination Reduction Trend for Stitched Composites using Quasi-Static Indentation Test

A novel empirical-based Delamination Reduction Trend (DRT) for stitched composites has been recently proposed. The DRT is capable of predicting the effective reduction in impact induced delamination area due to the influence of stitching. DRT simply relates two parameters: normalized delamination area and stitch fibre volume fraction, to characterize the effectiveness of stitching in impact damage suppression. This paper seeks to validate the DRT by using quasi-static indentation (QSI) test, which is considered analogous to low velocity impact test, due to similar structural response. Results from QSI test show good agreement with DRT. Furthermore, limitations in DRT have been established

Temporal-spatial analysis of severe acute respiratory syndrome among hospital inpatients

Background. We report the temporal-spatial spread of severe acute respiratory syndrome (SARS) among inpatients in a hospital ward during a major nosocomial outbreak and discuss possible mechanisms for the outbreak. Methods. All inpatients who had stayed in the same ward as the initial index case patient for any duration before isolation were recruited into a cohort and followed up to document the occurrence of SARS. The normalized concentration of virus-laden aerosols at different locations of the ward was estimated by use of computational fluid dynamics modeling. The attack rates in the various subgroups stratified by bed location were calculated. Multivariate Cox proportional hazards regression was used to document important risk factors. Results. The overall attack rate of SARS was 41% (30 of 74 subjects). It was 65%, 52%, and 18% in the same bay, adjacent bay, and distant bays, respectively (P = .001). Computation fluid dynamics modeling indicated that the normalized concentration of virus-laden aerosols was highest in the same bay and lowest in the distant bays. Cox regression indicated that staying in the ward on 6 or 10 March entailed higher risk, as well as staying in the same or adjacent bays. The epidemic curve showed 2 peaks, and stratified analyses by bed location suggested >1 generation of spread. Conclusions. The temporal-spatial spread of SARS in the ward was consistent with airborne transmission, as modeled by use of computational fluid dynamics. Infected health care workers likely acted as secondary sources in the latter phase of the outbreak. © 2005 by the Infectious Diseases Society of America. All rights reserved.published_or_final_versio

Progressive Damage in Stitched Composites under Impact Loading

Damage in carbon fibre reinforced plastics (CFRP) due to impact loading is an extremely complex phenomenon that comprises of multiple failure mechanisms like intra-laminar matrix cracks, interlaminar delamination, fibre pull-out and fibre fracture. In stitched composites, impact damage behavior is further complicated by the presence of through-thickness stitching [1, 2], which not only favorably increases mode I/II interlaminar strength [3, 4], but also inevitably creates geometrical defects like weak resin-rich pockets around stitch threads and misalignment of in-plane fibres. Computational modeling has been used to simulate progressive damage effectively [5]. However, the complexity of impact damage progression in stitched composites would need to be first understood and appreciated by physical experimental observations. In this study, quasi-static indentation (QSI) test is performed for the first time on stitched composites. QSI offers a good validation and comparison with low-velocity impact (LVI) test [6], and provides good understanding on damage progression in composite structures under impact loading. Damage initiation, propagation and ultimate failure are investigated due to the effect of stitching, particularly the influence of stitch density. Nondestructive evaluation (NDE) techniques namely ultrasonic c-scan analysis, x-ray radiography and xray micro computed tomography are employed to elucidate various damage mechanisms in stitched composites

Inconsistency of QED in the Presence of Dirac Monopoles

A precise formulation of $U(1)$ local gauge invariance in QED is presented, which clearly shows that the gauge coupling associated with the unphysical longitudinal photon field is non-observable and actually has an arbitrary value. We then re-examine the Dirac quantization condition and find that its derivation involves solely the unphysical longitudinal coupling. Hence an inconsistency inevitably arises in the presence of Dirac monopoles and this can be considered as a theoretical evidence against their existence. An alternative, independent proof of this conclusion is also presented.Comment: Extended and combined version, refinements added; 20 LaTex pages, Published in Z. Phys. C65, pp.175-18