100 research outputs found
Non-Clashing Teaching Maps for Balls in Graphs
Recently, Kirkpatrick et al. [ALT 2019] and Fallat et al. [JMLR 2023]
introduced non-clashing teaching and showed it to be the most efficient machine
teaching model satisfying the benchmark for collusion-avoidance set by Goldman
and Mathias. A teaching map for a concept class assigns a
(teaching) set of examples to each concept . A teaching
map is non-clashing if no pair of concepts are consistent with the union of
their teaching sets. The size of a non-clashing teaching map (NCTM) is the
maximum size of a , . The non-clashing teaching dimension
NCTD of is the minimum size of an NCTM for .
NCTM and NCTD are defined analogously, except the teacher may
only use positive examples.
We study NCTMs and NCTMs for the concept class
consisting of all balls of a graph . We show that the associated decision
problem {\sc B-NCTD} for NCTD is NP-complete in split, co-bipartite,
and bipartite graphs. Surprisingly, we even prove that, unless the ETH fails,
{\sc B-NCTD} does not admit an algorithm running in time
, nor a kernelization algorithm outputting a
kernel with vertices, where vc is the vertex cover number of .
These are extremely rare results: it is only the second (fourth, resp.) problem
in NP to admit a double-exponential lower bound parameterized by vc (treewidth,
resp.), and only one of very few problems to admit an ETH-based conditional
lower bound on the number of vertices in a kernel. We complement these lower
bounds with matching upper bounds. For trees, interval graphs, cycles, and
trees of cycles, we derive NCTMs or NCTMs for of size
proportional to its VC-dimension. For Gromov-hyperbolic graphs, we design an
approximate NCTM for of size 2.Comment: Shortened abstract due to character limi
Effect of MTU length on child-adult difference in neuromuscular fatigue
Purpose The purpose of this study was to compare the development and etiology
of neuromuscular fatigue of the knee extensor muscles (KE) at different
muscle-tendon unit (MTU) lengths during repeated maximal voluntary isometric
contractions (MVIC) between boys and men.Methods Twenty-two pre-pubertal boys
(9-11 years) and 22 men (18-30 years) performed three KE fatigue protocols at
short (SHORT), optimal (OPT) and long (LONG) MTU lengths, consisting of
repeating 5-s MVIC interspersed with 5-s passive recovery periods until torque
reached 60% of the initial MVIC torque. The etiology of neuromuscular fatigue
was identified using non-invasive methods such as surface electromyography,
near-infrared spectroscopy, magnetic nerve stimulation and twitch interpolation
technique.Results The number of repetitions was significantly lower in men at
OPT (14.83.2) and LONG (15.85.8) than boys (39.718.4 and 29.5
10.2, respectively; p<0.001), while no difference was found at SHORT
between both age groups (boys: 33.715.4, men: 40.914.2). At OPT and
LONG boys showed a lower reduction in the single potentiated twitch (Qtwpot)
and a greater decrease in the voluntary activation level (VA) than men. At
SHORT, both populations displayed a moderate Qtwpot decrement and a significant
VA reduction (p<0.001). The differences in maximal torque between boys and men
were almost twice greater at OPT (223.9 N.m) than at SHORT (123.3 N.m) and LONG
(136.5 N.m).Conclusion The differences in neuromuscular fatigue between
children and adults are dependent on MTU length. Differences in maximal torque
could underpin differences in neuromuscular fatigue between children and adults
at OPT and SHORT. However, at LONG these differences do not seem to be
explained by differences in maximal torque. The origins of this specific effect
of MTU length remain to be determined
Structure of the calcium pyrophosphate monohydrate phase (Ca2P2O7·H2O): towards understanding the dehydration process in calcium pyrophosphate hydrates
Calcium pyrophosphate hydrate (CPP, Ca2P2O7·nH2O) and calcium orthophosphate compounds (including apatite, octaÂcalcium phosphate etc.) are among the most prevalent pathological calcifications in joints. Even though only two dihydrated forms of CPP (CPPD) have been detected in vivo (monoclinic and triclinic CPPD), investigations of other hydrated forms such as tetraÂhydrated or amorphous CPP are relevant to a further understanding of the physicochemistry of those phases of biological interÂest. The synthesis of single crystals of calcium pyrophosphate monohydrate (CPPM; Ca2P2O7·H2O) by diffusion in silica gel at ambient temperature and the structural analysis of this phase are reported in this paper. Complementarily, data from synchrotron X-ray diffraction on a CPPM powder sample have been fitted to the crystal parameters. Finally, the relationship between the resolved structure for the CPPM phase and the structure of the tetraÂhydrated calcium pyrophosphate [beta] phase (CPPT-[beta]) is discussed
Sample Compression Schemes for Balls in Graphs
One of the open problems in machine learning is whether any set-family of VC-dimension d admits
a sample compression scheme of size O(d). In this paper, we study this problem for balls in graphs.
For balls of arbitrary radius r, we design proper sample compression schemes of size 4 for interval
graphs, of size 6 for trees of cycles, and of size 22 for cube-free median graphs. We also design
approximate sample compression schemes of size 2 for balls of ÎŽ-hyperbolic graphs
Maturation-related changes in the development and etiology of neuromuscular fatigue
International audiencePurpose: The aim of the present study was to investigate the role of maturation on the etiology of neuromuscular fatigue induced by repeated maximal voluntary isometric contractions (MVIC).Methods: Nine prepubertal boys (9.9â±â1.3 years), eight male adolescents (13.6â±â1.3 years) and eleven men (23.4â±â3.0 years) performed a series of repeated isometric MVICs of the knee extensors until the MVIC torque reached 60% of its initial value. Magnetic stimulations were delivered to the femoral nerve every five MVICs to follow the course of voluntary activation level (VA) and the potentiated twitch torque (Qtwpot).Results: Task failure was reached after 52.9â±â12.7, 42.6â±â12.5, and 26.6â±â6.3 repetitions in boys, adolescents and men, respectively. VA remained unchanged in men whereas it decreased significantly and similarly in boys and adolescents (pâ<â0.001). In contrast, Qtwpot remained unchanged in boys and decreased significantly less in adolescents than adults (pâ<â0.05).Conclusions: Children and adolescents experience less peripheral and more central fatigue than adults. However, adolescents experience more peripheral fatigue than children for a comparable amount of central fatigue. This finding supports the idea that the tolerance of the central nervous system to peripheral fatigue could increase during maturation
Mediating gel formation from structurally controlled poly(electrolytes) through multiple "head-to-body" electrostatic interactions
Tuning the chain-end functionality of a short-chain cationic homopolymer,
owing to the nature of the initiator used in the ATRP polymerisation step, can
be used to mediate the formation of a gel of this poly(electrolyte) in water.
While a neutral end group gives a solution of low viscosity, a highly
homogeneous gel is obtained with a phosphonate anionic moiety, as characterized
by rheometry and diffusion NMR. This novel type of supramolecular control over
poly(electrolytic) gel formation could find potential use in a variety of
applications in the field of electroactive materials
Children Exhibit a More Comparable Neuromuscular Fatigue Profile to Endurance Athletes Than Untrained Adults
The present study compared neuromuscular fatigue profiles between children, untrained adults and adult endurance athletes during repeated maximal muscle contractions. Eighteen prepubertal boys, 19 untrained men and 13 endurance male athletes performed 5-s maximal voluntary isometric knee extensor contractions (MVICs) interspersed with 5-s recovery until MVIC reached 60% of its initial value. Single and doublet magnetic stimulations were delivered to the femoral nerve to quantify the time course of potentiated twitch amplitude (Ttw,pot), high-frequency torque (T100Hz) and the low-to-high frequency torque ratio (T10Hz/T100Hz), i.e., indicators of peripheral fatigue. M-wave-normalized EMG amplitudes (EMG/M) and the maximal voluntary activation level (VA) were calculated to quantify central fatigue. Adults (15.9 ± 3.9 repetitions) performed fewer MVICs than children (40.4 ± 19.7) and endurance athletes (51.7 ± 19.6), however, no difference was observed between children and athletes (P = 0.13). Ttw,pot (âŒ52%, P < 0.001), T100Hz (âŒ39%, P < 0.001) and T10Hz/T100Hz (âŒ23%, P < 0.001) decreased only in adults. Similar decrements in vastus medialis and vastus lateralis EMG/M were observed in children and endurance athletes (range: 40â50%), and these were greater than in adults (âŒ15%). Whilst VA decreased more in children (-38.4 ± 22.5%, P < 0.001) than endurance athletes (-20.3 ± 10.1%, P < 0.001), it did not change in adults. Thus, children fatigued more slowly than adults and as much as endurance athletes. They developed less peripheral and more central fatigue than adults and, although central fatigue appeared somewhat higher in children than endurance athletes, both children and endurance athletes experienced greater decrements than adults. Therefore, children exhibit a more comparable neuromuscular fatigue profile to endurance athletes than adults
Precipitation in original Duralumin A-U4G versus modern 2017A alloy
Precipitation in Duralumin, a historic quaternary alloy of the type: AlâCuâMgâSi, was never fully studied nor observed by current electron microscopy techniques. This article presents the full characterization and comparison of two alloys: a Duralumin (A-U4G) from the 1950s collected on a vintage aircraft and its modern equivalent: a 2017A alloy. The as-received and peak-aging states were analysed with DSC, SAXS and TEM advanced techniques. It is shown that old Duralumin and modern 2017A present a similar nanoprecipitation in the as-received state and behave similarly upon artificial aging. As opposed to what has been reported in the past, three types of precipitates participating in hardening were found upon aging: Ξâ-Al2Cu, Qâ(Q)-AlCuMgSi and Ω-Al2Cu
Acute aquatic toxicity to zebrafish and bioaccumulation in marine mussels of antimony tin oxide nanoparticles
Antimony tin oxide (Sb2O5/SnO2) is effective in the absorption of infrared radiation for applications, such as skylights. As a nanoparticle (NP), it can be incorporated into films or sheets providing infrared radiation attenuation while allowing for a transparent final product. The acute toxicity exerted by commercial Sb2O5/SnO2 (ATO) NPs was studied in adults and embryos of zebrafish (Danio rerio). Our results suggest that these NPs do not induce an acute toxicity in zebrafish, either adults or embryos. However, some sub-lethal parameters were altered: heart rate and spontaneous movements. Finally, the possible bioaccumulation of these NPs in the aquacultured marine mussel Mytilus sp. was studied. A quantitative analysis was performed using single particle inductively coupled plasma mass spectrometry (sp-ICP-MS). The results indicated that, despite being scarce (2.31 Ă 106 ± 9.05 Ă 105 NPs/g), there is some accumulation of the ATO NPs in the mussel. In conclusion, commercial ATO NPs seem to be quite innocuous to aquatic organisms; however, the fact that some of the developmental parameters in zebrafish embryos are altered should be considered for further investigation. More in-depth analysis of these NPs transformations in the digestive tract of humans is needed to assess whether their accumulation in mussels presents an actual risk to humans.Fundação para a CiĂȘncia e Tecnologia | Ref. 2020.04021.CEECIN
Effects of sports drinks on the maintenance of physical performance during 3 tennis matches: a randomized controlled study
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