224 research outputs found
Biexciton stability in carbon nanotubes
We have applied the quantum Monte Carlo method and tight-binding modelling to
calculate the binding energy of biexcitons in semiconductor carbon nanotubes
for a wide range of diameters and chiralities. For typical nanotube diameters
we find that biexciton binding energies are much larger than previously
predicted from variational methods, which easily brings the biexciton binding
energy above the room temperature threshold.Comment: revtex4, final, twocolumn. to be published in Phys.Rev.Let. 5 pages 3
figure
Fluctuating work in coherent quantum systems: proposals and limitations
One of the most important goals in quantum thermodynamics is to demonstrate
advantages of thermodynamic protocols over their classical counterparts. For
that, it is necessary to (i) develop theoretical tools and experimental set-ups
to deal with quantum coherence in thermodynamic contexts, and to (ii) elucidate
which properties are genuinely quantum in a thermodynamic process. In this
short review, we discuss proposals to define and measure work fluctuations that
allow to capture quantum interference phenomena. We also discuss fundamental
limitations arising due to measurement back-action, as well as connections
between work distributions and quantum contextuality. We hope the different
results summarised here motivate further research on the role of quantum
phenomena in thermodynamics.Comment: As a chapter of: F. Binder, L. A. Correa, C. Gogolin, J. Anders, and
G. Adesso (eds.), "Thermodynamics in the quantum regime - Recent Progress and
Outlook", (Springer International Publishing). Second version: Misspell in
the title correcte
Mobility improvement in the first 6 postoperative weeks in orthogeriatric fracture patients
BACKGROUND Physical activity is a relevant outcome parameter in orthopedic surgery, that can be objectively assessed. Until now, there is little information regarding objective gait parameters in the orthogeriatric population. This study focuses on the first 6~weeks of postoperative rehabilitation, and delivers objective data about gait speed and step length in typical orthogeriatric fracture patterns. METHODS Thirty-one orthogeriatric fracture patients pertrochanteric femur fractures (PFF), femoral neck (FN), and proximal humerus fractures (PHF) were consecutively enrolled in a maximum care hospital in a prospective study design. All patients wore an accelerometer placed at the waist during the postoperative stay (24~h/d) and at 6-week follow-up, to measure real gait speed and step length. In addition, self-assessment of mobility (Parker mobility score) and activities of daily living (Barthel index) were collected at baseline, during the inpatient stay, and at 6-week follow-up. RESULTS During postoperative hospitalization, significantly higher gait speed (m/s) was observed in the PHF group (0.52 ± 0.27) compared with the FN group (0.36 ± 0.28) and PFF group (0.19 ± 0.28) (p < 0.05). Six~weeks postoperatively, gait speed improved significantly in all groups (PHF 0.90 ± 0.41; FN 0.72 ± 0.13; PFF 0.60 ± 0.23). Similarly, step length (m) differed between groups postoperatively FN 0.16 ± 0.13; PFF 0.12 ± 0.15; PHF 0.31 ± 0.05 (p < 0.005) and improved over time significantly (FN 0.47 ± 0.01; 0.39 ± 0.19; 0.50 ± 0.18). Self-assessment scores indicate that the majority of the patients had minor restrictions in mobility before the fracture. These values decreased immediately postoperatively and improved in the first 6~weeks, but did not reach the initial level. CONCLUSIONS Gait speed, step length, and self-assessment in terms of mobility and activities of daily living improve significantly in the first 6 postoperative weeks in orthogeriatric fracture patients. As very low postoperative mobility during hospitalization was observed, this collective shows great potential in postoperative rehabilitation regardless of their fracture pattern. For this reason, specific aftercare concepts similar to the {\textquotedbl}fast track{\textquotedbl} concepts in primary arthroplasty are crucial for orthogeriatric patients in clinical practice. LEVEL OF EVIDENCE Prospective cohort study, 2
Radiographic cortical thickness parameters as predictors of rotational alignment in proximal tibial shaft fractures: a cadaveric study
AIM The treatment of tibial fractures with an intramedullary nail is an established procedure. However, torsional control remains challenging using intraoperatively diagnostic tools. Radiographic tools such as the Cortical Step Sign (CSS) and the Diameter Difference Sign (DDS) may serve as tools for diagnosing a relevant malrotation. The aim of this study was to investigate the effect of torsional malalignment on CSS and DDS parameters and to construct a prognostic model to detect malalignment. METHODS A proximal tibial shaft fracture was set in human tibiae. Torsion was set stepwise from 0° to 30° in external and internal torsion. Images were obtained with a C-arm and transferred to a PC for measuring the medical cortical thickness (MCT), lateral cortical thickness (LCT), tibial diameter (TD) in AP and the anterior cortical thickness (ACT) as well as the posterior cortical thickness (PCT) and the transverse diameter (TD) of the proximal and the distal main fragment. RESULTS There were significant differences between the various degrees of torsion for each of the absolute values of the examined variables. The parameters with the highest correlation were TD, LCT and ACT. A model combining ACT, LCT, PCT and TD lateral was most suitable model in identifying torsional malalignment. The best prediction of clinically relevant torsional malalignment, namely 15°, was obtained with the TD and the ACT. CONCLUSION This study shows that the CSS and DDS are useful tools for the intraoperative detection of torsional malalignment in proximal tibial shaft fractures and should be used to prevent maltorsion
The second law and beyond in microscopic quantum setups
The Clausius inequality (CI) is one of the most versatile forms of the second
law. Although it was originally conceived for macroscopic steam engines, it is
also applicable to quantum single particle machines. Moreover, the CI is the
main connecting thread between classical microscopic thermodynamics and
nanoscopic quantum thermodynamics. In this chapter, we study three different
approaches for obtaining the CI. Each approach shows different aspects of the
CI. The goals of this chapter are: (i) To show the exact assumptions made in
various derivations of the CI. (ii) To elucidate the structure of the second
law and its origin. (iii) To discuss the possibilities each approach offers for
finding additional second-law like inequalities. (iv) To pose challenges
related to the second law in nanoscopic setups. In particular, we introduce and
briefly discuss the notions of exotic heat machines (X machines), and "lazy
demons".Comment: As a chapter of: F. Binder, L. A. Correa, C. Gogolin, J. Anders, and
G. Adesso (eds.), "Thermodynamics in the quantum regime - Recent Progress and
Outlook", (Springer International Publishing). v1 does not include references
to other book chapter
Long‑term results of the augmented PFNA: a prospective multicenter trial
Producción CientíficaPertrochanteric fractures are increasing and
their operative treatment remains under discussion. Failures
needing reoperations such as a cut-out are reported to
be high and are associated with multiple factors including
poor bone quality, poor fracture reduction and improper
implant placement. The PFNA® with perforated blade
offers an option for standardized cement augmentation
with a PMMA cement to provide more stability to the
fracture fixation. It remains unclear if the augmentation
of this implant does any harm in a longer time span. This
prospective multicenter study shows clinical and radiological
results with this implant with a mean follow-up time of
15 months
The T-pod is as stable as supraacetabular fixation using 1 or 2 Schanz screws in partially unstable pelvic fractures: a biomechanical study
Introduction: Unstable fractures of the pelvis remain the predominant cause of severe hemorrhage, shock and early death in severely injured patients. The use of pelvic binders has become increasingly popular, particularly in the preclinical setting. There is currently insufficient evidence available about the stability of the pelvic binder versus supraacetabular fixation using 1 or 2 Schanz screws. We aimed to analyze the stability of the pelvic binder and supraacetabular fixateurs using either 1 or 2 Schanz screws in a cadaver model of an induced pelvic B-type fracture.
Materials and methods: The study was undertaken in 7 human fresh-frozen cadaveric pelvises with induced AO-type B fractures. Three stabilization techniques were compared: T-POD (pelvic bandage), supraacetabular external fixator with 1 pin on each side and external fixator with 2 pins on each side. Stability and stiffness were analyzed in a biomechanical testing machine using a 5-step protocol with static and dynamic loading, dislocation data were retrieved by ultrasound sensors at the fracture sites.
Results: No significant differences in fracture fragment displacement were detected when using either the T-POD, a 1-pin external fixator or a 2-pin external fixator (P > 0.05). The average difference in displacement between the three methods was < 1 mm.
Conclusions: Pelvic binders are suitable for reduction of pelvic B-type fractures. They provide stability comparable to that of supraacetabular fixators, independently of whether 1 or 2 Schanz screws per side are used. Pelvic binders provide sufficient biomechanical stability for transferring patients without the need to first replace them with surgically applied external fixators. However, soft tissue irritation has to be taken into consideration and prolonged wear should be avoided.
Level of evidence: Level III
Standardised cement augmentation of the PFNA using a perforated blade: A new technique and preliminary clinical results. A prospective multicentre trial
Producción CientíficaPertrochanteric fractures are a rising major health-care problem in the elderly and their operative
stabilisation techniques are still under discussion. Furthermore, complications like cut-out are reported
to be high and implant failure often is associated with poor bone quality. The PFNA1 with perforated
blade offers a possibility for standardised cement augmentation using a polymethylmethacrylate
(PMMA) cement which is injected through the perforated blade to enlarge the load-bearing surface and
to diminish the stresses on the trabecular bone. The current prospective multicentre study was
undertaken to evaluate the technical performance and the early clinical results of this new device.
In nine European clinics, 59 patients (45 female, mean age 84.5 years) suffering from an osteoporotic
pertrochanteric fracture (Arbeitsgemeinschaft fu¨ r Osteosynthesefragen, AO-31) were treated with the
augmented PFNA1. Primary objectives were assessment of operative and postoperative complications,
whereas activities of daily living, pain, mobility and radiologic parameters, such as cement distribution
around the blade and the cortical thickness index, were secondary objectives.
The mean follow-up time was 4 months where we observed callus healing in all cases. The surgical
complication rate was 3.4% with no complication related to the cement augmentation. More than onehalf
of the patients reached their prefracture mobility level within the study period. A mean volume of
4.2 ml of cement was injected. We did not find any cut-out, cut through, unexpected blade migration,
implant loosening or implant breakage within the study period.
Our findings lead us to conclude that the standardised cement augmentation using the perforated
blade for pertrochanteric fracture fixation enhances the implant anchorage within the head–neck
fragment and leads to good functional results
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