Bandits Warm-up Cold Recommender Systems

We address the cold start problem in recommendation systems assuming no contextual information is available neither about users, nor items. We consider the case in which we only have access to a set of ratings of items by users. Most of the existing works consider a batch setting, and use cross-validation to tune parameters. The classical method consists in minimizing the root mean square error over a training subset of the ratings which provides a factorization of the matrix of ratings, interpreted as a latent representation of items and users. Our contribution in this paper is 5-fold. First, we explicit the issues raised by this kind of batch setting for users or items with very few ratings. Then, we propose an online setting closer to the actual use of recommender systems; this setting is inspired by the bandit framework. The proposed methodology can be used to turn any recommender system dataset (such as Netflix, MovieLens,...) into a sequential dataset. Then, we explicit a strong and insightful link between contextual bandit algorithms and matrix factorization; this leads us to a new algorithm that tackles the exploration/exploitation dilemma associated to the cold start problem in a strikingly new perspective. Finally, experimental evidence confirm that our algorithm is effective in dealing with the cold start problem on publicly available datasets. Overall, the goal of this paper is to bridge the gap between recommender systems based on matrix factorizations and those based on contextual bandits

The effects of dynamic and static stretching methods on speed, agility and power

INTRODUCTION: Warm-ups are integral to coaches’ and athletes’ preparations, yet current research and practice provides conflicting advice on the most effective warm-up procedure for aiding performance. The value of a warm-up is not in question but the role of static stretching within the warm-up is contentious. A number of studies have suggested that static stretching is detrimental to performance (Shrier, 2004), though these have not always employed stretching protocols that reflect those actually used by performers. Many athletes continue to include static stretching as part of their routine, often following a dynamic warm-up. The purpose of the study was to investigate, using realistic protocols, the effects on speed, agility and power of additional static stretching following a dynamic warm-up. METHOD: To date 16 University sports students (11 male, 5 female) have been recruited to the study, which was approved by the University ethics commitee. Following familiarisation with the warm-up methods and sports performance measures, all participants performed two warm-up protocols one week apart. The protocols concentrated on the quadriceps, hamstrings, gastrocnemius, soleus, gluteals, adductors and hip flexors. The Dynamic Warm-up (DW) protocol used a series of specific progresive exercises lasting 10 minutes over a distance of 20m with a jog recovery. The Dynamic Warm-up plus Static Stretching (DWS) protocol used the same DW protocol followed by a 5 minute period during which 7 stretches were held at a point of moderate discomfort for 20 seconds. After an intial rest period of 2 minutes the subjects performed a countermovement vertical jump (CMJ), 20m sprint and Illinios agility test. A one minute rest period was used between performance measures to mimic competitive performance. The order the performance measures were conducted were randomised for each subject; for an individual subject the order was maintained for both protocols. Paired t-tests were used to identify differences between the 3 performance measures over the two warm-up protocols, with a significance level of p ≤ 0.05. RESULTS & DISCUSSION: 20m sprint performance was significantly reduced (p=0.03) by the use of the DWS protocol (3.4 ± 0.32s, mean ± SD) when compared to DW only (3.29 ± 0.29s). The CMJ (DW =0.51 ± 0.09m vs DWS =0.48 ± 0.09m) and Illinois agility (DW =17.31 ±1.0s vs DWS =17.37 ±1.04s) performance showed no significant difference with the addition of static stretching. Previous studies have used static stretching for periods in excess of levels used in conventional warm-ups but the present study indicates that static stretching for as little as 20 seconds after a dynamic warm-up can reduce 20m sprinting performance. Possible mechanisms for this include a decrease in the stiffness of the musculotendinous unit and an acute neural inhibition leading to a decrease in muscle activation levels (Young, 2007). CONCLUSION: The use of static stretching following a dynamic warm-up decreased sprinting performance compared with the dynamic warm-up alone. Practitioners and athletes should use static stretching prior to performance with caution

Inspiratory muscle warm-up does not improve cycling time-trial performance

Purpose: This study examined the effects of an active cycling warm-up, with and without the addition of an inspiratory muscle warm-up (IMW), on 10-km cycling time-trial performance

Nuclear spin warm-up in bulk n-GaAs

We show that the spin-lattice relaxation in n-type insulating GaAs is dramatically accelerated at low magnetic fields. The origin of this effect, that cannot be explained in terms of well-known diffusion-limited hyperfine relaxation, is found in the quadrupole relaxation, induced by fluctuating donor charges. Therefore, quadrupole relaxation, that governs low field nuclear spin relaxation in semiconductor quantum dots, but was so far supposed to be harmless to bulk nuclei spins in the absence of optical pumping can be studied and harnessed in much simpler model environment of n-GaAs bulk crystal.Comment: 5 pages, 4 figure

The effects of postactivation potentiation on sprint and jump performance of male academy soccer players.

The purpose of this investigation was to evaluate the postactivation potentiation (PAP) effects of both dynamic and isometric maximum voluntary contractions (MVCs) on sprint and jump performance and establish whether PAP methods could be used effectively in warm up protocols for soccer players. Twelve male soccer players performed 4 warm up protocols in a cross-over, randomized, and counterbalanced design. In addition to a control warm up, subjects performed deadlift (5 repetitions at 5 repetitions maximum), tuck jump (5 repetitions), and isometric MVC knee extensions (3 repetitions for 3 s) as PAP treatments in an otherwise identical warm up protocol. After each treatment, the subjects underwent 3 10 m and 20 m sprints 4, 5, and 6 minutes post-warm up and 3 vertical jumps (VJ) at 7, 8, and 9 minutes post-warm up. Repeated measures analysis of variance showed no significant differences in the first 10 m (p = 0.258) and 20 m (p = 0.253) sprint and VJ (p = 0.703) performance and the average 10 m (p = 0.215), 20 m (p = 0.388), and VJ (p = 0.529) performance between conditions. There were also no significant differences in performance responses between the strongest and weakest subjects, but large variations in individual responses were found between the subjects. The findings suggest that there was no significant group PAP effect on sprint and jump performance after dynamic and isometric MVCs compared with a control warm up protocol. However, the large variation in individual responses (-7.1% to +8.2%) suggests PAP should be considered on an individual basis. Factors such as method, volume, load, recovery, and interindividual variability of PAP must be considered in the practical application of PAP and the rigorous research design of future studies to evaluate the potential for performance enhancement

Comparison of the effect of a Physical Education-Based Stretching Program applied during the Warm-Up, ColdDown and both periods on hamstring extensibility in Primary Schoolchildren.

Purpose. To compare the effects of a physical education-based stretching program applied during the warm-up, cold-down and both periods on hamstring extensibility in primary schoolchildren. Methods. A sample of 237 schoolchildren aged 7-12 years old (128 girls and 109 boys) from two primary school centres participated in the present study and met satisfactorily the inclusion and exclusion criteria. A cluster randomized controlled trial design was used. The classes balanced by grade were randomly assigned to the warm-up (n = 57), cold-down (n = 55), both periods (n = 61) or control groups (n = 64). During the physical education sessions, the students from the interventional groups performed a four-minute stretching program twice a week for eight weeks. The intervention program was applied during the warm-up (4 minutes), cold-down (4 minutes) and warm-up (2 minutes)-cold-down (2 minutes) for the warm-up, cold-down and both periods groups, respectively. Hamstring extensibility (estimated by the back-saver sit-and-reach test) was assessed at the beginning and at the end of the intervention program. Results. The one-way ANOVA (p 0.05). Conclusions. In order to develop students’ flexibility, PE teachers should apply stretching programs during the cold-down period. Due to the negative effect of static stretching on performance as previously found in the literature, it seems that PE teachers should improve students´ flexibility during the cool-down period of the sessions.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Pre-conference Warm Up

Michael Farris Smith reads from The Fighte

Twisting your melon: describing tricky movements on the page

Describes a warm-up exercise for drama students

IbM TPR Warm Up Game dalam Pembelajaran Bahasa Inggris Berbasis Pendidikan Karakter Bagi Guru-guru PAUD di Kecamatan Tembalang Semarang

Ilmu pengetahuan dan teknologi yang akan di transfer kepada HIMPAUDIKecamatan Tembalang Semarang adalah pelatihan bagi guru-guru PAUD dalamimplementasi TPR Warm Up Game dalam Pembelajaran Bahasa Inggris Berbasisendidikan Karakter bagi Guru-guru PAUD di Kecamatan Tembalang Semarangehingga guru-guru PAUD dapat menerapkan pengajaran bahasa Inggris yangmenyenangkan sesuai dengan kebutuhan anak. Ada tiga materi yang disampaikan dalampelatihan ini yaitu: (1) Pendidikan Karakter/Character Building, (2) Perkembangan danKreativitas Anak Usia dini, dan (3) Total Physical Response (TPR) Warm Up Game. elama pelatihan atau workshop guru-guru PAUD diberi pelatihan bagaimana mengintegrasikan pendidikan karakter dalam pembelajaran bahasa Inggris denganmenggunakan metode pembelajaran TPR Warm Up Game yang bertujuan untukmeningkatkan kreativitas anak usia dini. Guru-guru PAUD juga berlatih untukmengembangkan ide-ide mereka dalam pembelajaran bahasa Inggris dengan metode TPRWarm Up Game yang disesuaikan dengan kebutuhan anak usia dini dan juga kurikulumang ada di Taman Kanak-kanak ataupun PAUD

Effects of Myofascial Release and Dynamic Warm-up on Exercise Performance

Color poster with text, tables, and graphs.The purpose of this study was to compare the use of foam-rolling to dynamic warm-up on flexibility, power, speed, endurance, and balance in young recreationally active adults.University of Wisconsin--Eau Claire Office of Research and Sponsored Programs