Proton Decay Constraints on Low Scale AdS/CFT Unification

Dark matter candidates and proton decay in a class of models based on the AdS/CFT correspondence are discussed. We show that the present bound on the proton decay lifetime is inconsistent with ${\cal N} = 1$ SUSY, and strongly constrains ${\cal N} = 0$ non-SUSY, low scale trinification type unification of orbifolded AdS$\otimes S^5$ models.Comment: 10 page

Collisional Processes in Extrasolar Planetsimal Disks - Dust Clumps in Fomalhaut's Debris Disk

This paper presents a model for the outcome of collisions between planetesimals in a debris disk and assesses the impact of collisional processes on the structure and size distribution of the disk. The model is presented by its application to Fomalhaut's collisionally replenished dust disk; a recent 450 micron image of this disk shows a clump embedded within it with a flux ~5 per cent of the total. The following conclusions are drawn: (i) SED modelling is consistent with Fomalhaut's disk having a collisional cascade size distribution extending from bodies 0.2 m in diameter down to 7 micron-sized dust. (ii) Collisional lifetime arguments imply that the cascade starts with planetesimals 1.5-4 km in diameter. Any larger bodies must be predominantly primordial. (iii) Constraints on the timescale for the ignition of the cascade are consistent with these primordial planetesimals having a distribution that extends up to 1000km, resulting in a disk mass of 5-10 times the minimum mass solar nebula. (iv) The debris disk is expected to be intrinsically clumpy, since planetesimal collisions result in dust clumps. The intrinsic clumpiness of Fomalhaut's disk is below current detection limits, but could be detectable by future observatories such as the ALMA, and could provide the only way of determining the primordial planetesimal population. (v) The observed clump could have originated in a collision between two runaway planetesimals, both larger than 1400 km diameter. It is unlikely that we should witness such an event unless both the formation of these runaways and the ignition of the collisional cascade occurred within the last ~10 Myr. (vi) Another explanation for Fomalhaut's clump is that ~5 per cent of the planetesimals in the ring are trapped in 1:2 resonance with a planet orbiting at 80 AU.Comment: 21 pages, 13 figures, accepted by MNRA

Minimal Pati-Salam Model from String Theory Unification

We provide what we believe is the minimal three family ${\cal N} = 1$ SUSY and conformal Pati-Salam Model from type IIB superstring theory. This $Z_3$ orbifolded AdS$\otimes S^5$ model has long lived protons and has potential phenomenological consequences for LHC.Comment: 8 page

Design of aircraft turbine fan drive gear transmission system

The following basic types of gear reduction concepts were studied as being feasible power train systems for a low-bypass-ratio, single-spool, geared turbofan engine for general aircraft use: (1) single-stage external-internal reduction, (2) gears (offset shafting), (3) multiple compound idler gear system (concentric shafting), and (4) star gear planetary system with internal ring gear final output member (concentric shafting-counterrotation). In addition, studies were made of taking the accessories drive power off both the high-speed and low-speed shafting, using either face gears or spiral bevel gears. Both antifriction and sleeve-type bearings were considered for the external-internal and star-planet reduction concepts

Herschel evidence for disk flattening or gas depletion in transitional disks

Transitional disks are protoplanetary disks characterized by reduced near- and mid-infrared emission with respect to full disks. This characteristic spectral energy distribution indicates the presence of an optically thin inner cavity within the dust disk believed to mark the disappearance of the primordial massive disk. We present new Herschel Space Observatory PACS spectra of [OI] 63 micron for 21 transitional disks. Our survey complements the larger Herschel GASPS program "Gas in Protoplanetary Systems" (Dent et al. 2013) by quadrupling the number of transitional disks observed with PACS at this wavelength. [OI] 63 micron traces material in the outer regions of the disk, beyond the inner cavity of most transitional disks. We find that transitional disks have [OI] 63 micron line luminosities two times fainter than their full disk counterparts. We self consistently determine various stellar properties (e.g. bolometric luminosity, FUV excess, etc.) and disk properties (e.g. disk dust mass, etc.) that could influence the [OI] 63 micron line luminosity and we find no correlations that can explain the lower [OI] 63 micron line luminosities in transitional disks. Using a grid of thermo-chemical protoplanetary disk models, we conclude that either transitional disks are less flared than full disks or they possess lower gas-to-dust ratios due to a depletion of gas mass. This result suggests that transitional disks are more evolved than their full disk counterparts, possibly even at large radii.Comment: Accepted for publication in ApJ; 52 pages, 16 figures, 8 table

Closed timelike curves in asymmetrically warped brane universes

In asymmetrically warped spacetimes different warp factors are assigned to space and to time. We discuss causality properties of these warped brane universes and argue that scenarios with two extra dimensions may allow for timelike curves which can be closed via paths in the extra-dimensional bulk. In particular, necessary and sufficient conditions on the metric for the existence of closed timelike curves are presented. We find a six-dimensional warped metric which satisfies the CTC conditions, and where the null, weak and dominant energy conditions are satisfied on the brane (although only the former remains satisfied in the bulk). Such scenarios are interesting, since they open the possibility of experimentally testing the chronology protection conjecture by manipulating on our brane initial conditions of gravitons or hypothetical gauge-singlet fermions (sterile neutrinos) which then propagate in the extra dimensions.Comment: 24 pages, 2 figures; major corrections: CTC metric generalized from 5D to 6D, the new 6D metric satisfies the conclusions attributed (incorrectly) to the 5D metric in v

GASPS—A Herschel Survey of Gas and Dust in Protoplanetary Disks: Summary and Initial Statistics

We describe a large-scale far-infrared line and continuum survey of protoplanetary disk through to young debris disk systems carried out using the ACS instrument on the Herschel Space Observatory. This Open Time Key program, known as GASPS (Gas Survey of Protoplanetary Systems), targeted ∼250 young stars in narrow wavelength regions covering the [OI] fine structure line at 63 μm the brightest far-infrared line in such objects. A subset of the brightest targets were also surveyed in [OI]145 μm, [CII] at 157 μm, as well as several transitions of H_2O and high-excitation CO lines at selected wavelengths between 78 and 180 μm. Additionally, GASPS included continuum photometry at 70, 100 and 160 μm, around the peak of the dust emission. The targets were SED Class II–III T Tauri stars and debris disks from seven nearby young associations, along with a comparable sample of isolated Herbig AeBe stars. The aim was to study the global gas and dust content in a wide sample of circumstellar disks, combining the results with models in a systematic way. In this overview paper we review the scientific aims, target selection and observing strategy of the program. We summarise some of the initial results, showing line identifications, listing the detections, and giving a first statistical study of line detectability. The [OI] line at 63 μm was the brightest line seen in almost all objects, by a factor of ∼10. Overall [OI]63 μm detection rates were 49%, with 100% of HAeBe stars and 43% of T Tauri stars detected. A comparison with published disk dust masses (derived mainly from sub-mm continuum, assuming standard values of the mm mass opacity) shows a dust mass threshold for [OI]63 μm detection of ∼10^(-5) M_⊙. Normalising to a distance of 140 pc, 84% of objects with dust masses ≥10^(-5) M_⊙ can be detected in this line in the present survey; 32% of those of mass 10^(-6)–10^(-5) M_⊙, and only a very small number of unusual objects with lower masses can be detected. This is consistent with models with a moderate UV excess and disk flaring. For a given disk mass, [OI] detectability is lower for M stars compared with earlier spectral types. Both the continuum and line emission was, in most systems, spatially and spectrally unresolved and centred on the star, suggesting that emission in most cases was from the disk. Approximately 10 objects showed resolved emission, most likely from outflows. In the GASPS sample, [OI] detection rates in T Tauri associations in the 0.3–4 Myr age range were ∼50%. For each association in the 5–20 Myr age range, ∼2 stars remain detectable in [OI]63 μm, and no systems were detected in associations with age >20 Myr. Comparing with the total number of young stars in each association, and assuming a ISM-like gas/dust ratio, this indicates that ∼18% of stars retain a gas-rich disk of total mass ∼1 M_(Jupiter) for 1–4 Myr, 1–7% keep such disks for 5–10 Myr, but none are detected beyond 10–20 Myr. The brightest [OI] objects from GASPS were also observed in [OI]145 μm, [CII]157 μm and CO J = 18 - 17, with detection rates of 20–40%. Detection of the [CII] line was not correlated with disk mass, suggesting it arises more commonly from a compact remnant envelope

Project Towards No Drug Abuse: A Review of the Findings and Future Directions

Objective: To provide a review of the evidence from 3 experimental trials of Project Towards No Drug Abuse (TND), a senior high-school-based drug abuse prevention program.Methods: Theoretical concepts, subjects, designs, hypotheses, findings, and conclusions of these trials are presented. A total of 2,468 high school youth from 42 schools in southern California were surveyed.Results: The Project TND curriculum shows reductions in the use of cigarettes, alcohol, marijuana, hard drugs, weapon carrying, and victimization. Most of these results were replicated across the 3 trials. Conclusion: Project TND is an effective drug and violence prevention program for older teens, at least for one year follow-up