The phase plane of moving discrete breathers

We study anharmonic localization in a periodic five atom chain with quadratic-quartic spring potential. We use discrete symmetries to eliminate the degeneracies of the harmonic chain and easily find periodic orbits. We apply linear stability analysis to measure the frequency of phonon-like disturbances in the presence of breathers and to analyze the instabilities of breathers. We visualize the phase plane of breather motion directly and develop a technique for exciting pinned and moving breathers. We observe long-lived breathers that move chaotically and a global transition to chaos that prevents forming moving breathers at high energies.Comment: 8 pages text, 4 figures, submitted to Physical Review Letters. See http://www.msc.cornell.edu/~houle/localization

Acoustic Emission from crumpling paper

From magnetic systems to the crust of the earth, many physical systems that exibit a multiplicty of metastable states emit pulses with a broad power law distribution in energy. Digital audio recordings reveal that paper being crumpled, a system that can be easily held in hand, is such a system. Crumpling paper both using the traditional hand method and a novel cylindrical geometry uncovered a power law distribution of pulse energies spanning at least two decades: (exponent 1.3 - 1.6) Crumpling initally flat sheets into a compact ball (strong crumpling), we found little or no evidence that the energy distribution varied systematically over time or the size of the sheet. When we applied repetitive small deformations (weak crumpling) to sheets which had been previously folded along a regular grid, we found no systematic dependence on the grid spacing. Our results suggest that the pulse energy depends only weakly on the size of the paper regions responsible for sound production.Comment: 12 pages of text, 9 figures, submitted to Phys. Rev. E, additional information availible at http://www.msc.cornell.edu/~houle/crumpling

THE ACADEMIC IMPACT OF THE SYMPOSIUM ON ENDOSCOPY AND MINIMALLY INVASIVE SPINE SURGERY OF THE MEXICAN ASSOCIATION OF SPINE SURGEONS – AMCICO

ABSTRACT Introduction: The interest in spinal endoscopy is rising, particularly among younger spine surgeons. Formalized postgraduate training programs for endoscopic spinal surgery techniques are lacking behind. Methods: The authors performed a retrospective survey study amongst participants of the 2022 AMCICO endoscopic surgery symposium. Descriptive and correlative statistics were done on the surgeon’s responses recorded in multiple-choice questions. In addition, surgeons were asked about their clinical experience and preferences with spinal endoscopy, training background, the types of lumbar endoscopic decompression they perform by approach, and future training requirements. SPSS (version 27) statistical software package was used for data analysis. Descriptive statistic measures were used to count responses and calculate the mean, range, standard deviation, and percentages. In addition, chi-square statistics were used to determine the strength of the association between factors. Results: The online survey was accessed by 321 surgeons, of which 92 completed it (53.4%). Demographic data showed the majority of responding surgeons being orthopedic surgeons (73.6%) and under the age of 50 (69.2%), with over half (51.1%) having less than three months of formalized training in endoscopic spinal surgery techniques. Most surgeons practiced uni-portal (58.9%) versus bi-portal (3.4%) spinal endoscopy. The transforaminal approach (65.5%) was preferred over the interlaminar method (34.4%). The bi-portal technique was indicated almost exclusively for the lumbar spine (94.8%). For endoscopically assisted spinal fusions, a uni-portal approach was preferred by 72% of surgeons over a bi-portal procedure (24.5%). 84.1% of respondents were interested in navigation, of which 30.7% preferred optical over electromagnetic technology (18.2%). Robotics was of interest to 51.1% of survey participants. Respondents’ bias was estimated with course attendance assessments, with 37% of surgeons having attended all three days, 27.2% two days, and 16.3% one day. One-fifth of responding spine surgeons did not participate in any curriculum activities but completed the survey. The academic impact of the AMCICO endoscopy symposium was high, with 68.1% of respondents indicating interest in continued training and 61.1% of trainees ready to apply their newly acquired knowledge base to clinical practice. Conclusion: The interest in spinal endoscopy surgery techniques and protocols is high among AMCICO members. Many surgeons are interested in learning advanced endoscopic surgical techniques to integrate the technology into their surgical procedure portfolio to address common painful conditions of the degenerative spine beyond herniated discs and foraminal stenosis. The authors concluded that its academic impact was high based on the responses given by the participating surgeons. Level of evidence III; Retrospective study

Disturbance and the resilience of coupled carbon and nitrogen cycling in a north temperate forest

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96419/1/jgrg864.pd

Measuring serotonin synthesis: from conventional methods to PET tracers and their (pre)clinical implications

The serotonergic system of the brain is complex, with an extensive innervation pattern covering all brain regions and endowed with at least 15 different receptors (each with their particular distribution patterns), specific reuptake mechanisms and synthetic processes. Many aspects of the functioning of the serotonergic system are still unclear, partially because of the difficulty of measuring physiological processes in the living brain. In this review we give an overview of the conventional methods of measuring serotonin synthesis and methods using positron emission tomography (PET) tracers, more specifically with respect to serotonergic function in affective disorders. Conventional methods are invasive and do not directly measure synthesis rates. Although they may give insight into turnover rates, a more direct measurement may be preferred. PET is a noninvasive technique which can trace metabolic processes, like serotonin synthesis. Tracers developed for this purpose are α-[11C]methyltryptophan ([11C]AMT) and 5-hydroxy-L-[β-11C]tryptophan ([11C]5-HTP). Both tracers have advantages and disadvantages. [11C]AMT can enter the kynurenine pathway under inflammatory conditions (and thus provide a false signal), but this tracer has been used in many studies leading to novel insights regarding antidepressant action. [11C]5-HTP is difficult to produce, but trapping of this compound may better represent serotonin synthesis. AMT and 5-HTP kinetics are differently affected by tryptophan depletion and changes of mood. This may indicate that both tracers are associated with different enzymatic processes. In conclusion, PET with radiolabelled substrates for the serotonergic pathway is the only direct way to detect changes of serotonin synthesis in the living brain