Simplified vector-thread architectures for flexible and efficient data-parallel accelerators

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 165-170).This thesis explores a new approach to building data-parallel accelerators that is based on simplifying the instruction set, microarchitecture, and programming methodology for a vector-thread architecture. The thesis begins by categorizing regular and irregular data-level parallelism (DLP), before presenting several architectural design patterns for data-parallel accelerators including the multiple-instruction multiple-data (MIMD) pattern, the vector single-instruction multiple-data (vector-SIMD) pattern, the single-instruction multiple-thread (SIMT) pattern, and the vector-thread (VT) pattern. Our recently proposed VT pattern includes many control threads that each manage their own array of microthreads. The control thread uses vector memory instructions to efficiently move data and vector fetch instructions to broadcast scalar instructions to all microthreads. These vector mechanisms are complemented by the ability for each microthread to direct its own control flow. In this thesis, I introduce various techniques for building simplified instances of the VT pattern. I propose unifying the VT control-thread and microthread scalar instruction sets to simplify the microarchitecture and programming methodology. I propose a new single-lane VT microarchitecture based on minimal changes to the vector-SIMD pattern.(cont.) Single-lane cores are simpler to implement than multi-lane cores and can achieve similar energy efficiency. This new microarchitecture uses control processor embedding to mitigate the area overhead of single-lane cores, and uses vector fragments to more efficiently handle both regular and irregular DLP as compared to previous VT architectures. I also propose an explicitly data-parallel VT programming methodology that is based on a slightly modified scalar compiler. This methodology is easier to use than assembly programming, yet simpler to implement than an automatically vectorizing compiler. To evaluate these ideas, we have begun implementing the Maven data-parallel accelerator. This thesis compares a simplified Maven VT core to MIMD, vector-SIMD, and SIMT cores. We have implemented these cores with an ASIC methodology, and I use the resulting gate-level models to evaluate the area, performance, and energy of several compiled microbenchmarks. This work is the first detailed quantitative comparison of the VT pattern to other patterns. My results suggest that future data-parallel accelerators based on simplified VT architectures should be able to combine the energy efficiency of vector-SIMD accelerators with the flexibility of MIMD accelerators.by Christopher Francis Batten.Ph.D

The effect of smoking on survival and bone loss of implants with a fluoride-modified surface: a 2-year retrospective analysis of 1106 implants placed in daily practice

Aim: To compare survival and peri-implant bone loss of implants with a fluoride-modified surface in smokers and nonsmokers. Materials and Methods: Patient files of all patients referred for implant treatment from November 2004 to 2007 were scrutinized. All implants were placed by the same experienced surgeon (BC). The only inclusion criterion was a follow-up time of at least 2 years. Implant survival and bone loss were assessed by an external calibrated examiner (SV) comparing digital peri-apical radiographs taken during recall visits with the post-operative ones. Implant success was determined according to the international success criteria (Albrektsson et al. 1986). Survival of implants installed in smokers and nonsmokers were compared using the log-rank test. Both non-parametric tests and fixed model analysis were adopted to evaluate bone loss in smokers and nonsmokers. Results: 1106 implants in 300 patients (186 females; 114 males) with a mean follow-up of 31 months (SD 7.15; range 24-58) were included. 19 implants in 17 patients failed, resulting in an overall survival rate of 98.3% on implant level and 94.6% on patient level. After a follow-up period of 2 years, the CSR was 96.7% and 99.1% with the patient and implant as statistical unit respectively. Implant survival was significantly higher for nonsmokers compared to smokers (implant level p = 0.025; patient level p = 0.017). The overall mean bone loss was 0.34 mm (n = 1076; SD 0.65; range 0.00-7.10). Smokers lost significantly more bone compared to nonsmokers in the maxilla (0.74 mm; SD 1.07 vs 0.33 mm; SD 0.65; p < 0.001), but not in the mandible (0.25mm; SD 0.65 vs 0.22mm; SD 0.50; p = 0.298). Conclusion: The present study is the first to compare peri-implant bone loss in smokers and nonsmokers from the time of implant insertion (baseline) to at least 2 years of follow-up. Implants with a fluoride-modified surface demonstrated a high survival rate and limited bone loss. However, smokers are at higher risk to experience implant failure and more prone to show peri-implant bone loss in the maxilla. Whether this bone loss is predicting future biological complications remains to be evaluated

Influence of Implant Neck Design on Peri-Implant Tissue Dimensions: A Comparative Study in Dogs

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Abstract: This in vivo study assessed (hard and soft) peri-implant tissue remodeling around implants with micro-ring and open-thread neck designs placed in a dog model. Twenty histological sections corresponding to four different implant designs that were placed in America Foxhound dogs were obtained from previous studies. All the implants had been placed under identical conditions and were divided into four groups: Group A, micro-rings on implant neck plus 0.5 mm refined surface; Group B, micro-rings on implant neck; Group C, open-thread neck; and, Group D, double-spiral neck. Eight weeks after surgery, the integrated implants were removed and processed for histological examination. Crestal bone loss and bone-to-implant contact was greater for micro-ring necks than open-thread necks. Soft tissues showed significant differences on both buccal and lingual aspects, so that the distance from peri-implant mucosa to the apical portion of the barrier epithelium was smaller in the micro-ring groups. So, in spite of generating greater bone-to-implant contact, implants with micro rings produced more bone loss than open-thread implants. Moreover, the outcomes that were obtained IPX implants smooth neck design produced less bone loss in the cervical area, following by Facility implants when compared with the other open thread and microthreaded implant designs. Implant thread design can influence on bone remodeling in the cervical area, related to bundle bone preservation.Odontologí

Microgrid - The microthreaded many-core architecture

Traditional processors use the von Neumann execution model, some other processors in the past have used the dataflow execution model. A combination of von Neuman model and dataflow model is also tried in the past and the resultant model is referred as hybrid dataflow execution model. We describe a hybrid dataflow model known as the microthreading. It provides constructs for creation, synchronization and communication between threads in an intermediate language. The microthreading model is an abstract programming and machine model for many-core architecture. A particular instance of this model is named as the microthreaded architecture or the Microgrid. This architecture implements all the concurrency constructs of the microthreading model in the hardware with the management of these constructs in the hardware.Comment: 30 pages, 16 figure

Evaluation of a New Dental Implant Cervical Design in Comparison with a Conventional Design in an Experimental American Foxhound Model

This is the peer reviewed versión of the following article: "Evaluation of a New Dental Implant Cervical Design in Comparison with a Conventional Design in an Experimental American Foxhound Model ", which has been published in final form at [doi:10.3390/ma11040462],. This article May be used for non-comercial pipotes in accordance with Wiley Terms an Conditions for Use of Self-Archived Versions.Odontologí

Comparing the TiOblast and Osseospeed surfaces. Histomorphometric and histological analysis in humans

The aim of the present study was to compare two implant surfaces, the TiOblast (Astra Tech) surface, manufactured by blasting the surface and already present in literature and the Osseospeed (Astra Tech) surface, manufactured by blasting and treating the surface with fluoride ions and recently launched onto the market with the modified surfaces of the latest generation. This study is part of a more extensive research project whose protocol required the insertion of 10 couples of implants; thus in the present discussion partial data are being taken into consideration, with an eye at collecting more data in the future, regarding both microscopy and histomorphometric histological analysis on 5 couples of implants. The purpose of the study is to investigate how the modified surfaces of the latest generation can guarantee a greater osseointegration both from a qualitative and quantitative level compared to the surfaces presently used and that they may represent the first example of "bioactivity", that is, an active interaction with the processes of new bone formation and tissue healing

Effect of viscosities of dispersed and continuous phases in microchannel oil-in-water emulsification

Although many aspects of microchannel emulsification have been covered in literature, one major uncharted area is the effect of viscosity of both phases on droplet size in the stable droplet generation regime. It is expected that for droplet formation to take place, the inflow of the continuous phase should be sufficiently fast compared to the outflow of the liquid that is forming the droplet. The ratio of the viscosities was therefore varied by using a range of continuous and dispersed phases, both experimentally and computationally. At high viscosity ratio (eta (d)/eta (c)), the droplet size is constant; the inflow of the continuous phase is fast compared to the outflow of the dispersed phase. At lower ratios, the droplet diameter increases, until a viscosity ratio is reached at which droplet formation is no longer possible (the minimal ratio). This was confirmed and elucidated through CFD simulations. The limiting value is shown to be a function of the microchannel design, and this should be adapted to the viscosity of the two fluids that need to be emulsified

Radiographic and Prosthetic Assessment Prior to Implantoprosthetic Therapy

Jedan od osnovnih uvjeta uspješnosti terapije oseointegrirajućim usadcima jest dobro predkirurško planiranje. Svrha je ovoga rada prikazati na slučaju djelomične bezubosti u distalnom dijelu mandibule mogućnosti radiološke i protetske ocjene prije kirurškoga tretmana. Na modelu čeljusti učinjeno je dijagnostičko navoštavanje. Nakon toga izrađena je šablona iz vakuum termoplastične folije. Metalne kuglice poznatoga promjera stavljene su u pozicije navoštanih zuba kako bi se radiološkom tehnikom ocijenila mogućnost implantacije u predviđenim pozicijama. Učinjen je klasični ortopantomogram te na temelju njega i slojeviti tomogram s točnim presjecima mandibule na položajima budućih usadaka. Na temelju rendgenskih nalaza određen je položaj i duljina usadaka. Prikazan je klasičan dvofazni kirurški protokol te operacijska tehnika s intraoralnim pretprotetskim šablonama. Uporabljeni su usadci Astratech microthread koničnoga profila kako bi se promjerom usatka što više približili promjeru budućega zuba. Dužina usatka određena je u skladu s navedenom radiološkom raščlambom tako da je usadak na poziciji 35 kraći od usadaka 34 i 37 zbog anatomske pozicije foramena mentale. Pri kirurškome pozicioniranju usatka osim pozicije koja je određena šablonom usadci su u okomitome smjeru pozicionirani u skladu s biološkom širinom sluznice i u konačnici parodontološko estetskim zahtjevima. Rezultati prikazuju uspješnost terapije nakon dobra planiranja i pripreme. Prikazana je prednost slojevite tomografije u planiranju i određivanju anatomsko-morfoloških karakteristika donje čeljusti koja nam daje sigurnost u izboru dužine, a osobito širine usatka. Predkirurško planiranje je postupak kojime možemo predvidjeti položaj usatka i estetiku budućega protetskog rada te tako olakšati kirurški zahvat.One of the fundamental pre-conditions for successful therapy by osseo-integrating implants is good pre-surgical planning. The aim of this work is to present the possibilities of radiographic and prosthetic evaluation prior to surgical treatment in the case of partial edentulousness.in the distal part of the mandibula. Diagnostic wax-up is done on a model of the jaw. After which a pattern is made of vacuum thermoplastic foil. Metal pellets of known diameter are placed in the positions of the waxed-up teeth to enable radiographic evaluation of the possibility of implantation in the planned positions. Classical orthopantomography is performed on the basis of which a multi-layer tomogram is done with exact cross-sections of the mandibula in the positions of future implants. On the basis of radiographic findings the position and length of the implants are determined. The classical two-phase surgical protocol is described and surgical technique with intraoral pre-prosthetic patterns. Astratech microthread implants of conical profile are used to ensure that the implant diameter is as close as possible to the diameter of the future tooth. The length of an implant is determined in accordance with the cited radiographic analysis, so that the implant in position 35 is shorter in relation to implants 34 and 37, due to the anatomic position of the foramen mentale. During surgical positioning of implants, apart from the position which is defined by the pattern, in the vertical direction the implants are positioned in accordance with the biological width of the mucous membrane and finally with periodontal aesthetic requirements. The results show the success of the therapy following good planning and preparation. The advantage is shown of multi-layer tomography in planning and determining the anatomical-morphological characteristics of the lower jaw, which provides assurance in the choice of length and particularly the width of the implant. Pre-surgical planning is a procedure by which it is possible to foresee the position of an implant and aesthetics of future prosthetic work, and thus to facilitate the surgical intervention