33 research outputs found
Second law, entropy production, and reversibility in thermodynamics of information
We present a pedagogical review of the fundamental concepts in thermodynamics
of information, by focusing on the second law of thermodynamics and the entropy
production. Especially, we discuss the relationship among thermodynamic
reversibility, logical reversibility, and heat emission in the context of the
Landauer principle and clarify that these three concepts are fundamentally
distinct to each other. We also discuss thermodynamics of measurement and
feedback control by Maxwell's demon. We clarify that the demon and the second
law are indeed consistent in the measurement and the feedback processes
individually, by including the mutual information to the entropy production.Comment: 43 pages, 10 figures. As a chapter of: G. Snider et al. (eds.),
"Energy Limits in Computation: A Review of Landauer's Principle, Theory and
Experiments
Assessment of canal walls after biomechanical preparation of root canals instrumented with protaper universalTM rotary system
OBJECTIVE: The aim of this study was to examine the instrumented walls of root canals prepared with the ProTaper UniversalTM rotary system. MATERIAL AND METHODS: Twenty mesiobuccal canals of human first mandibular molars were divided into 2 groups of 10 specimens each and embedded in a muffle system. The root canals were transversely sectioned 3 mm short of the apex before preparation and remounted in their molds. All root canals were prepared with ProTaper UniversalTM rotary system or with NitiflexTM files. The pre and postoperative images of the apical thirds viewed with a stereoscopic magnifier (X45) were captured digitally for further analysis. Data were analyzed statistically by Fisher's exact test and Chi-square test at 5% significance level. RESULTS: The differences observed between the instrumented and the noninstrumented walls were not statistically significant (p<0.05). CONCLUSIONS: The NitiflexTM files and the ProTaper UniversalTM rotary system failed to instrument all the root canal walls
Leveraging Environmental Correlations: The Thermodynamics of Requisite Variety
Key to biological success, the requisite variety that confronts an adaptive
organism is the set of detectable, accessible, and controllable states in its environment.
We analyze its role in the thermodynamic functioning of information ratchets---a form of
autonomous Maxwellian Demon capable of exploiting fluctuations in an external information
reservoir to harvest useful work from a thermal bath. This establishes a quantitative
paradigm for understanding how adaptive agents leverage structured thermal environments for
their own thermodynamic benefit. General ratchets behave as memoryful communication
channels, interacting with their environment sequentially and storing results to an output.
The bulk of thermal ratchets analyzed to date, however, assume memoryless environments that
generate input signals without temporal correlations. Employing computational mechanics and
a new information-processing Second Law of Thermodynamics (IPSL) we remove these
restrictions, analyzing general finite-state ratchets interacting with structured
environments that generate correlated input signals. On the one hand, we demonstrate that a
ratchet need not have memory to exploit an uncorrelated environment. On the other, and more
appropriate to biological adaptation, we show that a ratchet must have memory to most
effectively leverage structure and correlation in its environment. The lesson is that to
optimally harvest work a ratchet's memory must reflect the input generator's memory.
Finally, we investigate achieving the IPSL bounds on the amount of work a ratchet can
extract from its environment, discovering that finite-state, optimal ratchets are unable to
reach these bounds. In contrast, we show that infinite-state ratchets can go well beyond
these bounds by utilizing their own infinite "negentropy". We conclude with an outline of
the collective thermodynamics of information-ratchet swarms