Body mass maximizes power output in human jumping: a strength-independent optimum loading behavior

It is well known that in vitro muscles maximize their power output when acting against a moderate resistance regarding their maximum strength. Similar behavior has been observed from in vivo muscular systems in both single-joint and most of the multi-joint maximum performance tasks. We refer to that phenomenon as a strength-dependent behavior, since the optimum external load that maximizes the mechanical power output of particular muscle(s) or neuro-musculoskeletal system corresponds to a certain percent of maximum strength. In this review paper, we present evidence that the optimum load in maximum vertical jumps is one’s own body mass, regardless of the strength of the lower limb muscles (i.e., the strength-independent behavior). Although the discussed phenomenon is still underexplored, we believe that several neuro-mechanical mechanisms are involved. Among these are a long-term adaptation of the muscular force–velocity relationship to the body weight and inertia, alteration of the jumping technique, load-specific muscle activation and jumping skills. Further exploration of the discussed strength-independent behavior of the lower limb muscles is of importance for refining various training and rehabilitation procedures, as well as for understanding the design and function of lower limb muscles.     

Knot theory realizations in nematic colloids

Nematic braids are reconfigurable knots and links formed by the disclination loops that entangle colloidal particles dispersed in a nematic liquid crystal. We focus on entangled nematic disclinations in thin twisted nematic layers stabilized by 2D arrays of colloidal particles that can be controlled with laser tweezers. We take the experimentally assembled structures and demonstrate the correspondence of the knot invariants, constructed graphs, and surfaces associated with the disclination loop to the physically observable features specific to the geometry at hand. The nematic nature of the medium adds additional topological parameters to the conventional results of knot theory, which couple with the knot topology and introduce order into the phase diagram of possible structures. The crystalline order allows the simplified construction of the Jones polynomial and medial graphs, and the steps in the construction algorithm are mirrored in the physics of liquid crystals.From the invention of ropes and textiles, up to the present day, knots have played a prominent role in everyday life, essential crafts, and artistic expression. Beyond the simple tying of strings, the intriguing irreducibility of knots has led to Kelvin’s vortex model of atoms, and, subsequently, a more systematic study of knots and links in the context of knot theory (1–3). As a branch of topology, knot theory is a developing field, with many unresolved questions, including the ongoing search for an algorithm that will provide an exact identification of arbitrary knots.As knots cannot be converted one into another without the crossing of the strands––a discrete singular event––knotting topologically stabilizes the structure. In physical fields, this coexistence of discrete and continuous phenomena leads to the stabilization of geometrically and topologically nontrivial high-energy excitations (4, 5). Examples of strand-like objects in physics that can be knotted include vortices in fluids (6–9), synthetic molecules (10, 11), DNA, polymer strands and proteins (12–14), electromagnetic field lines (15, 16), zero-intensity loci in optical interference patterns (17), wave functions in topological insulators (18), cosmic strings (19), and defects in a broad selection of ordered media (20–23).Nematic liquid crystals (NLC) are liquids with a local apolar orientational order of rod-like molecules. The director field, which describes the spatial variation of the local alignment axis, supports topological point and line defects, making it an interesting medium for the observation of topological phenomena (20, 24). Defect structures in NLC and their colloidal composites (25) have been extensively studied for their potential in self-assembly and light control (26), but also to further the theoretical understanding of topological phenomena in director fields (23, 27). Objects of interest include chiral solitons (28, 29), fields around knotted particles (30–35), and knotted defects in nematic colloids (36–42). Each of these cases is unique, as the rules of knot theory interact with the rules and restrictions of each underlying material and confinement. The investigation of knotted fields is thus a specialized topic where certain theoretical aspects of knot theory emerge in a physical context.In nematic colloids––dispersions of spherical particles confined in a twisted nematic (TN) cell––disclination lines entangle arrays of particles into “nematic braids,” which can be finely controlled by laser tweezers to form various linked and knotted structures (38, 39, 43). In this paper, we focus on the diverse realizations of knot theory in such nematic colloidal structures. We complement and extend the classification and analysis of knotted disclinations from refs. 32, 38, 40 with the direct application of graph and knot theory to polarized optical micrographs. We further analyze the nematic director with constructed Pontryagin–Thom surfaces and polynomial knot invariants, which enables a comprehensive topological characterization of the knotted nematic field based on experimental data and analytical tools. We use a λ-retardation plate to observe and distinguish differently twisted domains in the optical micrograph, which correspond to medial graphs of the represented knots and contribute to the Pontryagin–Thom construction of the nematic director. Finally, we explore the organization of the space of possible configurations on a selected rectangular particle array and discuss the observed hierarchy of entangled and knotted structures.     

The slow and infraslow oscillations of cortical neural network

ObjectiveIn this study we investigated the properties of infraslow oscillations (ISOs) ?0.05 Hz and delta frequency band in the patients during the epileptic discharges and in healthy persons who performed a variety of mental and physical tasks.MethodsThe EEG signals were recorded on the subjects who were divided into three groups. In the first group were patients with global epileptic seizures, while in the second group were patients with focal epileptic seizures. In the third group were healthy volunteers who performed different mental and physical tasks.ResultsBy analyzing EEG data of epileptic patients, we showed that frequency peak exists at 1.5 Hz which is typical for general and focal epileptic seizures. In the type of general epileptic discharges the role of the slow rhythms at 0.05 Hz, was particularly pronounced and their origin was in fluctuations of cortical neural network. The properties of parameter spectral coherency of ISOs in healthy persons point to their important role in brain functioning.ConclusionsOur results suggested that the role of ISOs could be extended, because they were detected in healthy human subjects during carrying out different tasks. Investigating the properties of parameter spectral coherency, we showed that in this case correlation between different regions of the brain was significantly modulated with ISOs.     

The relationship between surgical factors and margin status after breast-conservation surgery for early stage breast cancer

Background

The study's aim was to identify technical factors that are predictive of negative margins after breast-conserving surgery (BCS).

Methods

This was a retrospective, cohort study of patients who underwent BCS for early-stage cancer from 2000 to 2002. Pathological and specific surgical factors were compared with margin status. Univariate and multivariate regression analyses were performed.

Results

Four hundred eighty-nine cases were reviewed. The positive margin rate after the initial surgery was 26%. In univariate analysis, lobular histology, size, grade, multifocality, and the presence of EIC and LVI were associated with positive margins (P < .05). The absence of cavity margin dissection and specimen orientation labeling, the absence of a confirmed diagnosis, and smaller volumes of excision were also associated with positive margins (P < .05). In multivariate analysis, confirmed diagnosis, small tumor size, ductal histology, absence of LVI and multifocality, palpability, cavity margin dissection, and larger volumes of excision were predictors of negative margins.

Conclusions

This study shows that specific surgical factors are predictive of margin status. Both tumor and technical factors should be considered when planning BCS.     

Risk factors for treatment failure in renal suppurative infections

There are conflicting results of published studies about prognostic value of various factors in purulent renal infections. The purpose of this study was to identify and quantify potential risk factors for early and late treatment failure in such infections. A retrospective review of 75 renal suppurative infections, at three tertiary Serbian Clinics of Urology, was conducted. We considered numerous potential risk factors in a multivariate analysis. This series was comprised of 49 women and 26 men, with mean age of 56.7 years. There were 38 and 37 patients who experienced successful and unfavorable early treatment outcome, respectively. Overall mortality rate was 9.3%. Comorbidity [odds ratio (OR) = 1.6], complex suppurative pathological findings (OR = 3.6), presence of Pseudomonas spp. (OR = 6.7), multiple bacterial strains (OR = 2.7), and positive culture itself (OR = 3.6) were the predictors of poor early prognosis. A urological intervention and presence of pyonephrosis significantly increased the chance for good initial outcome (OR = 0.32 and 0.37, respectively). In the late treatment failure analysis presence of comorbidities (OR = 5.8) and treatment complications (OR = 7.5) significantly increased chance for fatal outcome. Patients’ baseline health status and complexity of suppuration itself were the most important predictors of clinical outcomes. Surgical drainage dominated over antimicrobial therapy.     

The use of magnetic resonance and MR angiography in the detection of cerebral infarction--a complication of pediatric bacterial meningitis

BACKGROUND: Association of both cerebral infarction and acute bacterial meningitis is more common in younger patients than in the elderly. The rate of mortality and the frequency of sequela are very high inspite of the use of modern antibiotic therapy. In more than 30% of the cases of childhood bacterial meningitis, both arterial and venous infarctions can occur. The aim of this study was to present the role of the use of magnetic resonance (MRI), and MR angiography (MRA) in the detection of bacterial meningitis in children complicated with cerebral infarctions. METHOD: In the Centre for MR, the Clinical Centre of Serbia, 25 patients with the diagnosis of bacterial meningitis, of which 9 children with cerebral infarction whose clinical condition deteriorated acutely, despite the antibiotic therapy, underwent MRI and MR angiography examination on a 1T scanner. Examination included the conventional spin-echo techniques with T1-weighted saggital and coronal, and T2- weighted axial and coronal images. Coronal fluid attenuated inversion recovery (FLAIR) and the postcontrast T1-weighted images in three orthogonal planes were also used. The use MR angiography was accomplished by the three-dimensional time-of-flight (3D TOF) technique. RESULTS: The findings included: multiple hemorrhagic infarction in 4 patients, multiple infarctions in 3 patients, focal infarction in 1 patient and diffuse infarction (1 patient). Common sites of involvement were: the frontal lobes, temporal lobes and basal ganglia. The majority of infarctions were bilateral. In 3 of the patients empyema was found, and in 1 patient bitemporal abscess was detected. In 8 of the patients MR angiography confirmed inflammatory vasculitis. CONCLUSION: Infarction is the most common sequela of severe meningitis in children. Since the complication of cerebral infarction influences the prognosis of meningitis, repetitive MRI examinations are very significant for the evaluation of the time course of vascular involvement. The use of MRI, especially FLAIR imaging, confirmed its value in the detection and determination of the site and the extent of cerebral infarction. Non-invasive technique of examination, 3D TOF MR angiography clearly shoud show the presence of inflammatory vasculitis.