Property-Driven Fence Insertion using Reorder Bounded Model Checking

Modern architectures provide weaker memory consistency guarantees than sequential consistency. These weaker guarantees allow programs to exhibit behaviours where the program statements appear to have executed out of program order. Fortunately, modern architectures provide memory barriers (fences) to enforce the program order between a pair of statements if needed. Due to the intricate semantics of weak memory models, the placement of fences is challenging even for experienced programmers. Too few fences lead to bugs whereas overuse of fences results in performance degradation. This motivates automated placement of fences. Tools that restore sequential consistency in the program may insert more fences than necessary for the program to be correct. Therefore, we propose a property-driven technique that introduces "reorder-bounded exploration" to identify the smallest number of program locations for fence placement. We implemented our technique on top of CBMC; however, in principle, our technique is generic enough to be used with any model checker. Our experimental results show that our technique is faster and solves more instances of relevant benchmarks as compared to earlier approaches.Comment: 18 pages, 3 figures, 4 algorithms. Version change reason : new set of results and publication ready version of FM 201

Incremental Cardinality Constraints for MaxSAT

Maximum Satisfiability (MaxSAT) is an optimization variant of the Boolean Satisfiability (SAT) problem. In general, MaxSAT algorithms perform a succession of SAT solver calls to reach an optimum solution making extensive use of cardinality constraints. Many of these algorithms are non-incremental in nature, i.e. at each iteration the formula is rebuilt and no knowledge is reused from one iteration to another. In this paper, we exploit the knowledge acquired across iterations using novel schemes to use cardinality constraints in an incremental fashion. We integrate these schemes with several MaxSAT algorithms. Our experimental results show a significant performance boost for these algo- rithms as compared to their non-incremental counterparts. These results suggest that incremental cardinality constraints could be beneficial for other constraint solving domains.Comment: 18 pages, 4 figures, 1 table. Final version published in Principles and Practice of Constraint Programming (CP) 201

LLVM2GOTO: A translator from LLVM IR to CPROVER IR

There are more than 700 programming languages. The number of softwares is astronomical. It is highly important to verify whether the software meets it's specification and it is safe. However, there are very few stable software verification tools. Translating a source program into verification intermediate representation(VIR) is an overhead for software verification community. If we trans- late compiler intermediate representation into VIR, the overhead of translating source to VIR is reduced and software written in programming languages supported by the compiler can be verified. LLVM2GOTO uses LLVM IR as compiler IR and CPROVER's goto IR as VIR. In the current implementation we support variable declaration, load, store, arithmetic, bitwise, typecast, branch and switch instructions are supported by LLVM2GOTO.

Imaging ultra-compact objects with radiatively inefficient accretion flows

Recent Event Horizon Telescope observations of M87* and Sgr A* strongly suggests the presence of supermassive black hole at their respective cores. In this work, we use the semi-analytic Radiatively Inefficient Accretion Flows (RIAF) model to investigate the resulting images of Joshi-Malafarina-Narayan (JMN-1) naked singularity and the Schwarzschild BH. We aim at choosing the JMN-1 naked singularity model and compare the synchrotron images with the Schwarzschild solution to search any distinct features which can distinguish the two objects and find alternative to the black hole solution. We perform general relativistic ray-tracing and radiative transfer simulations using Brahma code to generate synchrotron emission images utilising thermal distribution function for emissivity and absorptivity. We investigate effects in the images by varying inclination angle, disk width and frequency. The shadow images simulated by the JMN-1 model closely resemble those generated by the Schwarzschild black hole. When we compare these images, we find that the disparities between them are minimal. We conduct simulations using various plasma parameters, but the resulting images remain largely consistent for both scenarios. This similarity is evident in the horizontal cross-sectional brightness profiles of the two instances. Notably, the JMN-1 model exhibits slightly higher intensity in comparison to the Schwarzschild black hole. We conclude that JMN-1 presents itself as a viable substitute for the black hole scenario. This conclusion is not solely grounded in the fact that they are indistinguishable from their respective shadow observations, but also in the consideration that JMN-1 emerges as an end state of a continual gravitational collapse. This paradigm not only allows for constraints on spacetime but also provides a good probe for the nature of the central compact object.Comment: Accepted in A&A, 7 pages, 6 figures. arXiv admin note: text overlap with arXiv:2202.0058

Phase Transition Behavior of Cardinality and XOR Constraints

The runtime performance of modern SAT solvers is deeply connected to the phase transition behavior of CNF formulas. While CNF solving has witnessed significant runtime improvement over the past two decades, the same does not hold for several other classes such as the conjunction of cardinality and XOR constraints, denoted as CARD-XOR formulas. The problem of determining the satisfiability of CARD-XOR formulas is a fundamental problem with a wide variety of applications ranging from discrete integration in the field of artificial intelligence to maximum likelihood decoding in coding theory. The runtime behavior of random CARD-XOR formulas is unexplored in prior work. In this paper, we present the first rigorous empirical study to characterize the runtime behavior of 1-CARD-XOR formulas. We show empirical evidence of a surprising phase-transition that follows a non-linear tradeoff between CARD and XOR constraints

Integrating diversity into the medical curriculum

In the field of medical education, diversity refers to the presence and representation of persons from a diversified range of personal backgrounds, experiences, and characteristics across the student community, faculty members, and employees in the institution. The scope of diversity in medical education is immense and it plays a vital role in creating an effective learning environment. Once students are exposed to a group of diverse students and patients during their undergraduate training, there is a significant improvement in cultural competence, which becomes crucial in our mission to deliver patient-centered care. Considering the merits of diversity in the medical curriculum for medical students, there is an indispensable need to take specific measures to ensure that diversity is integrated in the curriculum, as it will also ensure the delivery of equitable and culturally competent medical care. As important is to ensure the integration of diversity into medical curriculum, equal importance has to be given to the measurement of various initiatives that have been taken to promote diversity in medical education. In conclusion, diversity in medical education is the need of the hour to create a fruitful learning environment for medical students. This calls for the need to take measures for the integration of diversity into the medical curriculum and subsequently identify strategies and indicators to measure and monitor the progress of diversity initiatives in medical institutions

Arthroscopic anterior cruciate ligament reconstruction with central quadriceps tendon bone (CQTB) graft: An outcome study in fifty Indian patients

Background: Arthroscopic ACL reconstruction using biologic autografts is the current gold standard in the management of symptomatic ACL tears. The commonly used BPTB (Bone-Patellar Tendon-Bone) and quadrupled hamstring tendon grafts have their own disadvantages. This study was conducted to evaluate the efficacy of CQTB (Central Quadriceps Tendon Bearing) graft as an autograft for ACL reconstruction in relieving instability in ACL deficient knees.Methods: 50 patients (45males; 5 females) with symptomatic ACL laxity, who underwent arthroscopic ACL reconstruction using the CQTB graft were followed up for 1 year. The functional improvement was analyzed by comparing the pre-operative Lysholm scores with those at 03 months, 06 months and 12 months post operatively. The objective improvement was analyzed comparing the Anterior Drawer and Lachman test grades pre-operatively and after 1 year follow up. The mean length of the graft and the post-operative morbidity were also noted.Results: The average Lysholm scores improved from a pre-operative value of 44.34 to 78.98,87.86 and 91.58 at 03months,06 months and 1 year respectively. (p<0.05; ANOVA). The number of patients with Grade I, II and III laxities on Anterior Drawer test improved from 01, 36 and 12 respectively to 43, 06 and 01 respectively 1 year after surgery (p<0.05; paired t test). The number of patients with Grade I, II and III laxities on Lachman test reduced from 1, 34 and 15 y to 39, 10 and 01 respectively. The average thickness of graft harvested was 9.21mm.Conclusions: CQTB autograft is a viable option along with other available autografts in its ability to reconstruct native ACL, without any hazards and additional complications