136879 research outputs found
Sort by
Replicated Agronomic Cotton Evaluations for the Texas Panhandle for 2021
No full textTexas Panhandle RACE Trial Report 202
Enhancing the Volumetric Effect of Point-Focusing Concentrating Solar Receivers via Partially Reflective Surfaces
Get PDFOne of the remaining challenges of point focusing concentrating solar power systems is the realization of a true volumetric receiver, one whose entire volume is utilized for the absorption of irradiance. Current state-of-the-art receivers (e.g., HiTRec-II and SolAir-200) have not demonstrated the volumetric effect, because of low radiation penetration within the absorber. Earlier works have noted that radiation penetration can be improved by increasing porosity (void fraction), but at the cost of reducing the convective heat transfer area. More recent works have succeeded at improving radiation penetration in volumetric absorbers by axially grading the porosity of the structure, but those designs are complex and share the issue of manufacturability. Nevertheless, the improvements are notable and justify the pursuit of true volumetric receivers. This work discusses the conceptual design and numerical evaluation of a true volumetric receiver achieved by applying different reflectivity distributions to the irradiated surfaces to improve radiation penetration.
The square honeycomb receiver structure was reduced to a single channel to allow for detailed modelling of radiative phenomena. Monte Carlo ray tracing was used to model external irradiance and the conventional direct integration approach was used to model mutual irradiance. This radiative model was coupled with a 3-dimensional heat transfer model and a laminar flow model for a complete description of the problem. Furthermore, the relationship between the axial reflectivity distribution and relevant design parameters like porosity and residence time are explored via parametric sweeps, with solar-to-thermal efficiency exit gas temperature and the volumetric effect ratio as the monitored responses. This work was completed using COMSOL Multiphysics��.
The base case parametric study showed that the optimal parameters for a Silicon Carbide uniform reflectivity receiver are those of the HiTRec-II. Both varied reflectivity receiver cases considered exhibited an improvement in performance parameters for the same average emissivity of the base case. The best performance was achieved by a wall-varied reflectivity receiver, where every two walls were assigned a certain emissivity based on the amount of radiation they intersect. This receiver design is expected to achieve an increase of 5.2%, 6.1% and 8.2% in the exit gas temperature, thermal efficiency and volumetric effect, respectively, compared to the HiTRec-II
Sleeping Among Us Issue 1
No full textNot dated.This publication may contain explicit sexual literary descriptions and/or artistic depictions.A Slash "Highlander" zine
Cache Design and Analysis for Mitigating Hardware Security in Multicore Systems
No full textSecurity in computing systems has been considered one of the greatest challenges due to the ever changing threat landscape, the complexity of systems, the presence of vulnerabilities, and a multitude of other factors. Security issues can cause billion-dollar damage and can expose private information to the public. Hardware security, in particular, has become a new territory for exploitation, including the recent discovery of transient execution attacks such as Spectre and Meltdown. They reveal the perils of transient execution in modern processors with out-of-order (O3) and speculative execution. Consequently, numerous researchers are dedicated to improving the security of computing systems.
Furthermore, Spectre and Meltdown have reshaped memory safety. Historically, memory safety issues were attributed to software bugs and human errors, leading software security experts to develop defenses such as bound checking and sandboxing. However, it is crucial to recognize that transient instructions, arising from mispredicted branches, can bypass these software defenses, accessing privileged data and transmitting it through cache side channels.
In addition to hardware security, a program���s calling context serves crucial functions in various use cases like profiling, debugging, optimization, and security monitors. They rely on uniquely encoded calling contexts for easy identification and consistency across runs. Existing encoding methods often lack this uniqueness and consistency, requiring users to add additional steps for their needs.
To mitigate the transient execution attacks, we develop ReViCe, a secure cache design to get rid of the side effect so that cache side channel is no longer available. We introduce a victim cache to restore the cache states from misspeculation and a jitter to hide the existence of cache lines installed by speculative request. For memory safety, we present a uniform defense against both software and hardware memory safety violation by profiling and checking program invariants. We observe that most of the memory locations of a program are accessed by only a handful of instructions during normal executions. These "good" instructions can be formulated for the corresponding memory locations at the current calling context as invariants of the program. Based on the observation, we present WHISTLE which extends a CPU and cache design to profile and check invariants at runtime with reasonable overhead. Last, we identify an inefficiency of existing calling context encoding schemes used by WHISTLE and present a new calling context encoding (DCCE), a faster encoding scheme for clients to improve their runtime performance