| 16971. |
- Mesgarzadeh, Behzad
(författare)
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Circuit Techniques for On-Chip Clocking and Synchronization
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Today’s microprocessors with millions of transistors perform high-complexity computing at multi-gigahertz clock frequencies. The ever-increasing chip size and speed call for new methodologies in clock distribution network. Conventional global synchronization techniques exhibit many drawbacks in the advanced VLSI chips such as high-speed microprocessors. A significant percentage of the total power consumption in a microprocessor is dissipated in the clock distribution network. Also since the chip dimensions increase, clock skew management becomes very challenging in the framework of conventional methodology. Long interconnect delays limit the maximum clock frequency and become a bottleneck for future microprocessor design. In such a situation, new alternative techniques for synchronization in system-on-chip are demanded.This thesis presents new alternatives for traditional clocking and synchronization methods, in which, speed and power consumption bottlenecks are treated. For this purpose, two new techniques based on mesochronous synchronization and resonant clocking are investigated. The mesochronous synchronization technique deals with remedies for skew and delay management. Using this technique, clock frequency up to 5 GHz for on-chip communication is achievable in 0.18-μm CMOS process. On the other hand the resonant clocking solves significant power dissipation problem in the clock network. This method shows a great potential in power saving in very large-scale integrated circuits. According to measurements, 2.3X power saving in clock distribution network is achieved in 130-nm CMOS process. In the resonant clocking, oscillator plays a crucial role as a clock generator. Therefore an investigation about oscillators and possible techniques for jitter and phase noise reduction in clock generators has been done in this research framework. For this purpose a study of injection locking phenomenon in ring oscillators is presented. This phenomenon can be used as a jitter suppression mechanism in the oscillators. Also a new implementation of the DLL-based clock generators using ring oscillators is presented in 130-nm CMOS process. The measurements show that this structure operates in the frequency range of 100 MHz-1.5 GHz, and consumes less power and area compared to the previously reported structures. Finally a new implementation of a 1.8-GHz quadrature oscillator with wide tuning range is presented. The quadrature oscillators potentially can be used as future clock generators where multi-phase clock is needed.
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| 16972. |
- Meshkian, Rahele, et al.
(författare)
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W-Based Atomic Laminates and Their 2D Derivative W1.33C MXene with Vacancy Ordering
- 2018
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 30:21
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Tidskriftsartikel (refereegranskat)abstract
- Structural design on the atomic level can provide novel chemistries of hybrid MAX phases and their MXenes. Herein, density functional theory is used to predict phase stability of quaternary i-MAX phases with in-plane chemical order and a general chemistry (W 2/3 M 2 1/3 ) 2 AC, where M 2 = Sc, Y (W), and A = Al, Si, Ga, Ge, In, and Sn. Of over 18 compositions probed, only two—with a monoclinic C2/c structure—are predicted to be stable: (W 2/3 Sc 1/3 ) 2 AlC and (W 2/3 Y 1/3 ) 2 AlC and indeed found to exist. Selectively etching the Al and Sc/Y atoms from these 3D laminates results in W 1.33 C-based MXene sheets with ordered metal divacancies. Using electrochemical experiments, this MXene is shown to be a new, promising catalyst for the hydrogen evolution reaction. The addition of yet one more element, W, to the stable of M elements known to form MAX phases, and the synthesis of a pure W-based MXene establishes that the etching of i-MAX phases is a fruitful path for creating new MXene chemistries that has hitherto been not possible, a fact that perforce increases the potential of tuning MXene properties for myriad applications.
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| 16973. |
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| 16974. |
- Metcalfe, Travis S., et al.
(författare)
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Asteroseismology and Spectropolarimetry of the Exoplanet Host Star Lambda Serpentis
- 2023
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Ingår i: Astronomical Journal. - : Institute of Physics (IOP). - 0004-6256 .- 1538-3881. ; 166:4
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Tidskriftsartikel (refereegranskat)abstract
- The bright star lambda Ser hosts a hot Neptune with a minimum mass of 13.6 M & OPLUS; and a 15.5 day orbit. It also appears to be a solar analog, with a mean rotation period of 25.8 days and surface differential rotation very similar to the Sun. We aim to characterize the fundamental properties of this system and constrain the evolutionary pathway that led to its present configuration. We detect solar-like oscillations in time series photometry from the Transiting Exoplanet Survey Satellite, and we derive precise asteroseismic properties from detailed modeling. We obtain new spectropolarimetric data, and we use them to reconstruct the large-scale magnetic field morphology. We reanalyze the complete time series of chromospheric activity measurements from the Mount Wilson Observatory, and we present new X-ray and ultraviolet observations from the Chandra and Hubble space telescopes. Finally, we use the updated observational constraints to assess the rotational history of the star and estimate the wind braking torque. We conclude that the remaining uncertainty on the stellar age currently prevents an unambiguous interpretation of the properties of lambda Ser, and that the rate of angular momentum loss appears to be higher than for other stars with a similar Rossby number. Future asteroseismic observations may help to improve the precision of the stellar age.
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| 16975. |
- Meurling, Lisbet, et al.
(författare)
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Comparison of high- and low equipment fidelity during paediatric simulation team training : a case control study
- 2014
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Ingår i: BMC Medical Education. - : Springer Science and Business Media LLC. - 1472-6920. ; 14, s. 221-
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Tidskriftsartikel (refereegranskat)abstract
- Background: High-fidelity patient simulators in team training are becoming popular, though research showing benefits of the training process compared to low-fidelity models is rare. We explored in situ training for paediatric teams in an emergency department using a low-fidelity model (plastic doll) and a high-fidelity paediatric simulator, keeping other contextual factors constant. The goal was to study differences in trainees' and trainers' performance along with their individual experiences, during in situ training, using either a low-fidelity model or a high-fidelity paediatric simulator.Methods: During a two-year period, teams involved in paediatric emergency care were trained in groups of five to nine. Each team performed one video-recorded paediatric emergency scenario. A case control study was undertaken in which 34 teams used either a low-fidelity model (n = 17) or a high-fidelity paediatric simulator (n = 17). The teams' clinical performances during the scenarios were measured as the time elapsed to prescribe as well as deliver oxygen. The trainers were monitored regarding frequency of their interventions. We also registered trainees' and trainers' mental strain and flow experience.Results: Of 225 trainees' occasions during 34 sessions, 34 trainer questionnaires, 163 trainee questionnaires, and 28 videos, could be analyzed. Time to deliver oxygen was significantly longer (p = 0.014) when a high-fidelity simulator was used. The trainees' mental strain and flow did not differ between the two types of training. The frequency of trainers interventions was lower (p < 0.001) when trainees used a high-fidelity simulator; trainers' perceived mental strain was lower (< 0.001) and their flow experience higher (p = 0.004) when using high-fidelity simulator.Conclusions: Levels of equipment fidelity affect measurable performance variables in simulation-based team training, but trainee s' individual experiences are similar. We also note a reduction in the frequency of trainers' interventions in the scenarios as well as their mental strain, when trainees used a high-fidelity simulator.
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| 16976. |
- Meyer, H.F., et al.
(författare)
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Overview of physics studies on ASDEX Upgrade
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- The ASDEX Upgrade (AUG) programme, jointly run with the EUROfusion MST1 task force, continues to significantly enhance the physics base of ITER and DEMO. Here, the full tungsten wall is a key asset for extrapolating to future devices. The high overall heating power, flexible heating mix and comprehensive diagnostic set allows studies ranging from mimicking the scrape-off-layer and divertor conditions of ITER and DEMO at high density to fully non-inductive operation (q 95 = 5.5, ) at low density. Higher installed electron cyclotron resonance heating power 6 MW, new diagnostics and improved analysis techniques have further enhanced the capabilities of AUG. Stable high-density H-modes with MW m-1 with fully detached strike-points have been demonstrated. The ballooning instability close to the separatrix has been identified as a potential cause leading to the H-mode density limit and is also found to play an important role for the access to small edge-localized modes (ELMs). Density limit disruptions have been successfully avoided using a path-oriented approach to disruption handling and progress has been made in understanding the dissipation and avoidance of runaway electron beams. ELM suppression with resonant magnetic perturbations is now routinely achieved reaching transiently . This gives new insight into the field penetration physics, in particular with respect to plasma flows. Modelling agrees well with plasma response measurements and a helically localised ballooning structure observed prior to the ELM is evidence for the changed edge stability due to the magnetic perturbations. The impact of 3D perturbations on heat load patterns and fast-ion losses have been further elaborated. Progress has also been made in understanding the ELM cycle itself. Here, new fast measurements of and E r allow for inter ELM transport analysis confirming that E r is dominated by the diamagnetic term even for fast timescales. New analysis techniques allow detailed comparison of the ELM crash and are in good agreement with nonlinear MHD modelling. The observation of accelerated ions during the ELM crash can be seen as evidence for the reconnection during the ELM. As type-I ELMs (even mitigated) are likely not a viable operational regime in DEMO studies of 'natural' no ELM regimes have been extended. Stable I-modes up to have been characterised using -feedback. Core physics has been advanced by more detailed characterisation of the turbulence with new measurements such as the eddy tilt angle - measured for the first time - or the cross-phase angle of and fluctuations. These new data put strong constraints on gyro-kinetic turbulence modelling. In addition, carefully executed studies in different main species (H, D and He) and with different heating mixes highlight the importance of the collisional energy exchange for interpreting energy confinement. A new regime with a hollow profile now gives access to regimes mimicking aspects of burning plasma conditions and lead to nonlinear interactions of energetic particle modes despite the sub-Alfvénic beam energy. This will help to validate the fast-ion codes for predicting ITER and DEMO.
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| 16977. |
- Meyer, H., et al.
(författare)
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Overview of progress in European medium sized tokamaks towards an integrated plasma-edge/wall solution
- 2017
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Ingår i: Nuclear Fusion. - : Institute of Physics Publishing (IOPP). - 0029-5515 .- 1741-4326. ; 57:10
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Tidskriftsartikel (refereegranskat)abstract
- Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads to tolerable heat and particle loads on the wall is a major challenge. The new European medium size tokamak task force (EU-MST) coordinates research on ASDEX Upgrade (AUG), MAST and TCV. This multi-machine approach within EU-MST, covering a wide parameter range, is instrumental to progress in the field, as ITER and DEMO core/pedestal and SOL parameters are not achievable simultaneously in present day devices. A two prong approach is adopted. On the one hand, scenarios with tolerable transient heat and particle loads, including active edge localised mode (ELM) control are developed. On the other hand, divertor solutions including advanced magnetic configurations are studied. Considerable progress has been made on both approaches, in particular in the fields of: ELM control with resonant magnetic perturbations (RMP), small ELM regimes, detachment onset and control, as well as filamentary scrape-off-layer transport. For example full ELM suppression has now been achieved on AUG at low collisionality with n = 2 RMP maintaining good confinement H-H(98,H-y2) approximate to 0.95. Advances have been made with respect to detachment onset and control. Studies in advanced divertor configurations (Snowflake, Super-X and X-point target divertor) shed new light on SOL physics. Cross field filamentary transport has been characterised in a wide parameter regime on AUG, MAST and TCV progressing the theoretical and experimental understanding crucial for predicting first wall loads in ITER and DEMO. Conditions in the SOL also play a crucial role for ELM stability and access to small ELM regimes.
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| 16978. |
- Meyer, H., et al.
(författare)
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Overview of progress in European medium sized tokamaks towards an integrated plasma-edge/wall solution
- 2017
-
Ingår i: Nuclear Fusion. - : Institute of Physics Publishing (IOPP). - 0029-5515 .- 1741-4326. ; 57:10
-
Tidskriftsartikel (refereegranskat)abstract
- Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads to tolerable heat and particle loads on the wall is a major challenge. The new European medium size tokamak task force (EU-MST) coordinates research on ASDEX Upgrade (AUG), MAST and TCV. This multi-machine approach within EU-MST, covering a wide parameter range, is instrumental to progress in the field, as ITER and DEMO core/pedestal and SOL parameters are not achievable simultaneously in present day devices. A two prong approach is adopted. On the one hand, scenarios with tolerable transient heat and particle loads, including active edge localised mode (ELM) control are developed. On the other hand, divertor solutions including advanced magnetic configurations are studied. Considerable progress has been made on both approaches, in particular in the fields of: ELM control with resonant magnetic perturbations (RMP), small ELM regimes, detachment onset and control, as well as filamentary scrape-off-layer transport. For example full ELM suppression has now been achieved on AUG at low collisionality with n = 2 RMP maintaining good confinement H-H(98,H-y2) approximate to 0.95. Advances have been made with respect to detachment onset and control. Studies in advanced divertor configurations (Snowflake, Super-X and X-point target divertor) shed new light on SOL physics. Cross field filamentary transport has been characterised in a wide parameter regime on AUG, MAST and TCV progressing the theoretical and experimental understanding crucial for predicting first wall loads in ITER and DEMO. Conditions in the SOL also play a crucial role for ELM stability and access to small ELM regimes.
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| 16979. |
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| 16980. |
- Mezuk, Briana, et al.
(författare)
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Beyond Access : Characteristics of the Food Environment and Risk of Diabetes
- 2016
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Ingår i: American Journal of Epidemiology. - : Oxford University Press (OUP). - 0002-9262 .- 1476-6256. ; 183:12, s. 37-1129
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Tidskriftsartikel (refereegranskat)abstract
- Characteristics of the built environment, including access to unhealthy food outlets, are hypothesized to contribute to type 2 diabetes mellitus (T2D). Swedish nationwide registry data on 4,718,583 adults aged 35-80 years living in 9,353 neighborhoods, each with at least 1 food outlet, were geocoded and linked to commercial registers (e.g., restaurants and grocery stores). Multilevel logistic regression was used to examine the prospective relationship between characteristics of the food environment and T2D from 2005 to 2010. Relative access to health-harming food outlets was associated with greater likelihood of both prevalent and incident T2D in a curvilinear manner, with the highest risk being observed for environments in which one-third of outlets were health-harming. Relative to individuals whose food environment did not change, those who moved into areas with more health-harming food outlets had higher odds of developing T2D (odds ratio = 3.67, 95% confidence interval: 2.14, 6.30). Among those who did not move, living in an area that gained relative access to health-harming food outlets was also associated with higher odds of T2D (odds ratio = 1.72, 95% confidence interval: 1.27, 2.33). These results suggest that local food environment, including changes that result in greater access to unhealthy food outlets, is associated with T2D.
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