Mermera: Non-Coherent Distributed Shared Memory for Parallel Computing

The proliferation of inexpensive workstations and networks has prompted several researchers to use such distributed systems for parallel computing. Attempts have been made to offer a shared-memory programming model on such distributed memory computers. Most systems provide a shared-memory that is coherent in that all processes that use it agree on the order of all memory events. This dissertation explores the possibility of a significant improvement in the performance of some applications when they use non-coherent memory. First, a new formal model to describe existing non-coherent memories is developed. I use this model to prove that certain problems can be solved using asynchronous iterative algorithms on shared-memory in which the coherence constraints are substantially relaxed. In the course of the development of the model I discovered a new type of non-coherent behavior called Local Consistency. Second, a programming model, Mermera, is proposed. It provides programmers with a choice of hierarchically related non-coherent behaviors along with one coherent behavior. Thus, one can trade-off the ease of programming with coherent memory for improved performance with non-coherent memory. As an example, I present a program to solve a linear system of equations using an asynchronous iterative algorithm. This program uses all the behaviors offered by Mermera. Third, I describe the implementation of Mermera on a BBN Butterfly TC2000 and on a network of workstations. The performance of a version of the equation solving program that uses all the behaviors of Mermera is compared with that of a version that uses coherent behavior only. For a system of 1000 equations the former exhibits at least a 5-fold improvement in convergence time over the latter. The version using coherent behavior only does not benefit from employing more than one workstation to solve the problem while the program using non-coherent behavior continues to achieve improved performance as the number of workstations is increased from 1 to 6. This measurement corroborates our belief that non-coherent shared memory can be a performance boon for some applications

Photon-Photon Collision: Simultaneous Observation of Wave-Particle Characteristics of Light

The proposed paper presents the analysis of electromagnetic waves meeting at a point in terms of their particle characteristics. The observation that light beams moves un-deviated when encountered at a point, which is commonly justified on the wave characteristics of light, is now presented as momentum and wavelength exchange phenomenon of photon collision. Theoretical and mathematical justification of photon’s inter-collision, on the basis of their quasi-point particle behavior is offered and the observation of the non-variation of wavelength of light beams is explained. Thus, the observation of light’s non-deviation at the crossing point is explained as momentum exchange phenomenon on the basis of particle characteristics of light. Keywords: Basic Quantum Mechanics, Bohr’s Complementary Principle, Collision Mechanic

Using Warp to Control Network Contention in Mermera

Parallel computing on a network of workstations can saturate the communication network, leading to excessive message delays and consequently poor application performance. We examine empirically the consequences of integrating a flow control protocol, called Warp control [Par93], into Mermera, a software shared memory system that supports parallel computing on distributed systems [HS93]. For an asynchronous iterative program that solves a system of linear equations, our measurements show that Warp succeeds in stabilizing the network's behavior even under high levels of contention. As a result, the application achieves a higher effective communication throughput, and a reduced completion time. In some cases, however, Warp control does not achieve the performance attainable by fixed size buffering when using a statically optimal buffer size. Our use of Warp to regulate the allocation of network bandwidth emphasizes the possibility for integrating it with the allocation of other resources, such as CPU cycles and disk bandwidth, so as to optimize overall system throughput, and enable fully-shared execution of parallel programs.NSF (IRI-8910195, IRI-9041581, CDA-8920936, CCR-9204284

Twin Circumflex Coronary Artery with anomalous origin from left main trunk — a rare variant

Coronary artery anomaly in form of dual origin of the circumflex artery is a rare anomaly. Though mostly described as having separate origin, both arising from left main coronary as twin circumflex artery itself has not been reported so far. Here we report a case of 57-year old male patient who had presented with ST elevation anterior wall myocardial infarction. His angiogram revealed left main trunk which was giving a left circumflex artery (LCx). On further coursing, left main trunk was trifurcating into left anterior descending artery (LAD), ramus intermedius and second left circumflex artery. Second circumflex branch was giving larger obtuse marginal branch while right coronary artery was smooth, non-dominant, and normal flowing artery. There was discrete eccentric stenosis with critical lesion in proximal LAD for which patient refused any intervention. Based on angiographic findings, it was diagnosed as a twin circumflex, both arising from left main trunk as one coming before the bifurcation while another after the bifurcation. An extensive search of literature and to the best of our knowledge, such type of anomaly is being reported for the first time

Unraveling and Entrapment leading to acute loss of jailed wire and its long term follow-up: case report

Jailed wire technique i.e wiring of the side branch (SB) before main vessel (MV) stenting is recommended to keep it open when the SB is deemed important ( > 2mm). Rarely, it becomes difficult to retrieve the jailed wire behind the stent and it may suffer fracture or entrapment, although exceedingly rare. It may be asymptomatic or can lead to abrupt closure of side branch resulting into periprocedural myocardial infarction. Here, we report a case of 56-old male who had undergone percutaneous coronary intervention (PCI) of proximal left anterior descending artery in 2012 during which jailed balance middle weight wire (BMW, Abott Vascular, USA) of diagonal branch got unravelled and entrapped. As patient was asymptomatic, he was conservatively managed. 6-years later, he suffered acute inferior wall myocardial infarction with complete heart block. Primary angioplasty of totally occluded right coronary artery was done with 3x38 mm Xience prime stent (Everolimus eluting stent; Abott vascular, USA). In coronary angiography of left system, left anterior descending and diagonal branches were completely patent. The fractured and retained jailed wire was still in diagonal branch with no displacement in comparison with previous coronary angiography. The patient was discharged in stable cardiac condition with appropriate follow up advise. To the best of our knowledge, this is the longest follow up of entrapped, and fractured BMW wire

„Dystalna ochrona farmakologiczna” przez podanie diltiazemu do pomostu naczyniowego w ramach leczenia wstępnego podczas interwencji w obrębie pomostu naczyniowego z żyły odpiszczelowej

Percutaneous coronary intervention (PCI) of vein graft lesions is associated with a high risk of peri-procedural myocardial infarction and greater mortality than routine native coronary intervention. Embolic protection devices have been advocated to reduce the risk of distal embolisation during vein graft PCI. Here, we report the case of a 72 year-old diabetic male smoker who had coronary artery bypass surgery three years previously who presented with acute coronary syndrome. Repeat coronary angiography revealed patent grafts except for a discrete eccentric critical lesion in ostium of saphenous vein graft to obtuse marginal. The lesion was crossed using a 0.014” runthrough wire (Terumo, Japan). Intragraft diltiazem (5 mg) was administered through the guiding catheter each time before predilatation and stenting (total dose = 30 mg). It was finally stented by deploying a 3.5 × 23 mm Xience Prime everolimus-eluting stent (Abbott, USA) at 13 atm pressure achieving TIMI III flow. He was discharged the next day with acetylsalicylic acid — 75 mg/day, ticagrelor — 90 mg twice daily, atorvastatin — 40 mg/day, metoprolol — 100 mg/day, and ramipril — 5 mg/day. The patient has been doing extremely well since then, with regular follow-ups at our institute.Przezskórna interwencja wieńcowa (PCI) w obrębie wszczepionego pomostu żylnego wiąże się z wysokim ryzykiem okołozabiegowego zawału serca i większą śmiertelnością niż rutynowe zabiegi tego typu w naczyniach natywnych. Zaleca się stosowanie urządzeń zabezpieczających przed zatorami w celu obniżenia ryzyka odległych zatorów w trakcie PCI w pomoście żylnym. Autorzy przedstawili przypadek 72-letniego pacjenta, aktywnego palacza, z ostrym zespołem wieńcowym, u którego 3 lata wcześniej wykonano chirurgiczne pomostowanie aortalno-wieńcowe. Powtórna koronarografia wykazała drożność stentu poza nieciągłą ekscentryczną krytyczną zmianą w miejscu połączenia pomostu z żyły odpiszczelowej z gałęzią brzeżną. Przez zwężenie przeprowadzono prowadnik angioplastyczny 0,014” typu runthrough (Terumo, Japonia). Przed każdą predylacją balonową i implantacją stentu do pomostu podawano diltiazem (5 mg) przez cewnik prowadzący (łączna dawka = 30 mg). Ostatecznie w miejscu zwężenia umieszczono i rozprężono stent uwalniający ewerolimus Xience Prime 3,5 × 23 mm (Abbott, USA), stosując ciśnienie 13 atm. Uzyskano przepływ TIMI III. Pacjenta wypisano następnego dnia z zaleceniem przyjmowania następujących leków: kwasu acetylosalicylowego — 75 mg/dobę, tikagreloru — 90 mg 2 razy/dobę, atorwastatyny — 40 mg/dobę, metoprololu — 100 mg/dobę i ramiprilu — 5 mg/dobę. Od czasu zabiegu chory czuł się bardzo dobrze i regularnie zgłaszał się na wizyty kontrolne do placówki autorów

Ostre zapadnięcie się całkowicie rozprężonego stentu III generacji w trakcie przezskórnej interwencji wieńcowej w obrębie rozwidlenia tętnic

Acute stent recoil or radial collapse of a stent is a rare phenomenon leading to subsequent acute stent thrombosis or in-stent restenosis as delayed sequelae. Reduced strut thickness, a larger stent/vessel ratio, and a larger balloon/stent ratio are factors leading to stent recoil. Here, we report a case of acute recoil or radial collapse of Promus Element Plus, a third-generation everolimus-eluting stent with thin stent struts in a 66 year-old male who underwent bifurcation percutaneous coronary intervention of left anterior descending artery (LAD) and diagonal branch (D1). Following kissing balloon inflation at 16 atm pressure after deployment of stents in LAD and D1, acute radial collapse of stent in proximal LAD was noted. It was successfully bailed out by further multiple, short sequential inflations using same size noncompliant balloon. Acute radial collapse probably occurred due to inflation at higher pressure with an oversized balloon, and relatively thin struts of the stent.Ostre zmniejszenie średnicy stentu lub zapadnięcie się stentu to rzadkie zjawisko, którego następstwem jest ostra zakrzepica w stencie lub późniejsze powikłanie w postaci restenozy w obrębie stentu. Czynnikami przyczyniającymi się do zmniejszenia średnicy stentu są mniejsza grubość rozpórek, wyższy współczynnik średnica stentu/średnica referencyjna naczynia oraz wyższy współczynnik średnica balonu/średnica stentu. Autorzy przedstawili przypadek ostrego zmniejszenia średnicy stentu lub zapadnięcia się stentu Promus Element Plus — stentu III generacji uwalniającego ewerolimus, z cienkimi rozpórkami — u 66-letniego pacjenta, u którego wykonano przezskórną interwencję wieńcową w obrębie rozwidlenia gałęzi międzykomorowej przedniej (LAD) i gałęzi diagonalnej D1. Po napełnieniu balonów (jednocześnie użyto 2 balonów — technika kissing balloon) pod ciśnieniem 16 atm i rozprężeniu stentów umieszczonych w LAD i D1 zaobserwowano ostre zapadnięcie się stentu w proksymalnym odcinku LAD. Sytuację udało się uratować, kilkakrotnie napełniając balon w krótkich sekwencjach. Zastosowano niepodatny balon o tym samym rozmiarze. Przyczynami ostrego zapadnięcia się stentu były przypuszczalnie napełnienie balonu o zbyt dużym rozmiarze z zastosowaniem zbyt wysokiego ciśnienia oraz stosunkowo cienkie rozpórki stentu