44 research outputs found
Defects and glassy dynamics in solid He-4: Perspectives and current status
We review the anomalous behavior of solid He-4 at low temperatures with
particular attention to the role of structural defects present in solid. The
discussion centers around the possible role of two level systems and structural
glassy components for inducing the observed anomalies. We propose that the
origin of glassy behavior is due to the dynamics of defects like dislocations
formed in He-4. Within the developed framework of glassy components in a solid,
we give a summary of the results and predictions for the effects that cover the
mechanical, thermodynamic, viscoelastic, and electro-elastic contributions of
the glassy response of solid He-4. Our proposed glass model for solid He-4 has
several implications: (1) The anomalous properties of He-4 can be accounted for
by allowing defects to freeze out at lowest temperatures. The dynamics of solid
He-4 is governed by glasslike (glassy) relaxation processes and the
distribution of relaxation times varies significantly between different
torsional oscillator, shear modulus, and dielectric function experiments. (2)
Any defect freeze-out will be accompanied by thermodynamic signatures
consistent with entropy contributions from defects. It follows that such
entropy contribution is much smaller than the required superfluid fraction, yet
it is sufficient to account for excess entropy at lowest temperatures. (3) We
predict a Cole-Cole type relation between the real and imaginary part of the
response functions for rotational and planar shear that is occurring due to the
dynamics of defects. Similar results apply for other response functions. (4)
Using the framework of glassy dynamics, we predict low-frequency yet to be
measured electro-elastic features in defect rich He-4 crystals. These
predictions allow one to directly test the ideas and very presence of glassy
contributions in He-4.Comment: 33 pages, 13 figure
Performance Issues in U.S.–China Joint Ventures
Based on an in-depth study of U.S.-China joint ventures, this article offers some insights into the performance of such international business relationships. While the conventional literature treats government as an amorphous aspea of the political-legal environment, in this case government is an active participant and influence in the performance of international joint ventures (UVs). It has both a constraining and enabling effect on LJV structure, strategy, and performance. For example, limits can be placed on ownership shares of joint ventures and on prices of the output. At the same time, government can cooperate with LJVs and foreign parent companies by creating partners for foreign parent companies, acting as major customers, and improving financial performance by lowering taxes
Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries
Background
Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres.
Methods
This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries.
Results
In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia.
Conclusion
This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries
Plastic properties of solid 4He probed by a moving wire:viscoelastic and stochastic behavior under high stress
We present measurements of a thin wire moving through solid 4He. Measurements were made over a wide temperature range at pressures close to the melting curve. We describe the new experimental technique and present preliminary measurements at relatively high driving forces (stresses) and velocities (strain rates). The wire moves by plastic deformation of the surrounding solid facilitated by quantum tunneling of vacancies and the motion of defects. In the bcc phase we observe very pronounced viscoelastic effects with relaxation times spanning several orders of magnitude. In the hcp phase we observe stochastic step-like motion of the wire. During the step, the wire can move at extremely high velocities. On cooling, the wire ceases to move at a temperature of around 1 K. We are unable to detect any motion at lower temperatures, down to below 10 mK