Collider Searches for Long-Lived Particles Beyond the Standard Model

Experimental tests of the Standard Model of particle physics (SM) find excellent agreement with its predictions. Since the original formation of the SM, experiments have provided little guidance regarding the explanations of phenomena outside the SM, such as the baryon asymmetry and dark matter. Nor have we understood the aesthetic and theoretical problems of the SM, despite years of searching for physics beyond the Standard Model (BSM) at particle colliders. Some BSM particles can be produced at colliders yet evade being discovered, if the reconstruction and analysis procedures not matched to characteristics of the particle. An example is particles with large lifetimes. As interest in searches for such long-lived particles (LLPs) grows rapidly, a review of the topic is presented in this article. The broad range of theoretical motivations for LLPs and the experimental strategies and methods employed to search for them are described. Results from decades of LLP searches are reviewed, as are opportunities for the next generation of searches at both existing and future experiments.Comment: 79 pages, 36 figures, submitted to Progress in Particle and Nuclear Physic

Pedagogical Agents in Interactive Multimedia Modules: Issues of Variability

AbstractThis paper introduces the pedagogical agents and describes its characteristics and roles in multimedia modules. It will also include examples of the use of pedagogical agents in previous studies and effective use of pedagogical agents on learning. Next, pedagogical agent variability in terms of physical (ethnicity, gender, image, voice) and internal features (roles, communication and competency) will be discussed in the context of its impact on learners’ diversity. This is then followed by a discussion and suggestions for further research regarding the effective use of pedagogical agent in multimedia modules

Electrodeposition and Properties of Tin Seleno Sulphide

Thin film semiconductors such as tin seleno sulphide films are considered important technological materials because of their potential applications in solar cells, infrared detectors and lasers. These thin films can be prepared by electrodeposition because of its simple, low cost and easy to control parameters. In this research, tin seleno sulphide thin films have been electrodeposited potentiostatically from aqueous solution containing SnCl₂, Na₂SeO₃ and Na₂S₂O₃ on titanium substrate. Disodium salt of ethylenediaminetetraacetic acid (Na₂-EDT A) was used as a complexant to improve the adhesion of the deposited film on the substrate. Cyclic voltammetry was performed to elucidiate the electrodic processes occurred and determine the potential range for electrodeposition. The effect of parameters such as bath temperatures, the presence of EDT A, deposition potentials, electrolytes concentrations, deposition times, pH, and annealing temperatures on the film properties were studied. The deposited films were characterized by powder X-ray diffiaction (PXRD), scanmng electron microscopy (SEM), energy dispersive X-ray analysis (ED AX) and linear sweep photovoltammetry (LSPV). The band gap energy and transition type were determined from optical absorbance data. PXRD results showed the formation of polycrystalline orthorhombic crystal structure of SnSe₀.₅S₀.₅ with strong (111) being the most intense orientation. SEM micrographs revealed the morphological nature of the deposit which is depended on the deposition condition. EDAX results showed that less sulfur was deposited for the samples. All films prepared in this study showed rectifying behaviour in cathodic polarization regime signifying p-type conduction. A good quality tin seleno sulphide film was obtained from equal volume mixture of 0.005 M Sn-EDTA, 0.0025 M Na2Se03 and 0.0025 M Na₂S₂O₃ solutions at potential -0.70 V in the presence of 0.010 MEDTA. Binary phase of SnS2 was found present in films deposited at more negative potentials than -0.70 V. The presence of EDT A has improved the quality of the samples. Increasing the bath temperature improve the crystallinity, morphology and photosensitivity of the films. The electrodeposition is most suitable to be carried out at 60°C. However, when bath temperature is increased to 70°C, the grain size and surface coverage of the deposits was reduced, which may due to dissolution of deposit because of high temperature. Increasing the deposition time allowed more material to be deposited onto the substrate and the most suitable deposition time was found to be 60 min. pH 1.0 was fovund to be the optimum condition to prepare tin seleno sulphide. The photosensitivity and crystallinity of the films decreased when pH 1.5 and pH 2.0 was used. Annealing at 400 DC for 20 min could improve the crystallinity of the films. The energy gap is around 1.20 eV with indirect transition type as determined by optical absorption data

Torque characteristics of high speed steel twist drills

The drill is the most efficient tool used by machinists, for in no other tool is the cutting surface as large in proportion to the cross sectional area of the body or part that is its real support. Drills have shared evolutionary developments from carbon steels to high speed steels and from flat to twist drills. Many investigations have been made on the twist drills, but due to the majority of their work being based on the size of drills from 1/2 to 1-1/2 inches or larger, there is a dearth of published data on the general problem of drills of smaller sizes, such as the diameter of drills smaller than 1/2 inch in diameter. Therefore, the object of this investigation is to determine the torque characteristics of certain commercial small drills and to evaluate the effect of various factors on the torque --Introduction, page 1

Towards an assay for allelic inactivation of vomeronasal receptor genes in mouse

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Biology, 1998.Includes bibliographical references (leaves 17-19).by Tien-Yi Lee.S.M