Residual opening of hydraulic fractures filled with compressible proppant

In hydraulic stimulations of oil and gas wells, injection of proppant (or small particles) is normally needed to avoid the closure of the created fractures under confining stresses. The residual openings of these fractures determine the efficiency and, in general, the success of the hydraulic stimulations. Despite the vast number of papers devoted to fluid driven fractures and hydraulic stimulation procedures, there has not been much research conducted on residual fracture profiles. This problem is characterised by a strong non-linearity and represents a challenge for numerical modelling. In this paper a simple semi-analytical method for calculating the residual openings of fractures partially filled with proppant is developed. It is based on the Distributed Dislocation Technique and Terzaghi's classical consolidation model. One of the results of simulations indicates that the proppant distribution and its mechanical properties have a significant influence on the residual fracture profiles. © 2013 Elsevier Ltd.Luiz Bortolan Neto, Andrei Kotouso

Amniotic fl uid embolism in an HIV-positive parturient

We present a case of a parturient infected with human immunode ciency virus, who developed amniotic fluid embolism during the delivery of her twins by elective Caesarean section. Our management and the available literature are briefly discussed, and consideration is given to a possible association between the two pathologies.Keywords: amniotic fluid embolism; anaphylaxis; human immunode  ciency viru

DEVELOPMENT AND VALIDATION OF A SYSTEM FOR POLING FORCE MEASUREMENT IN CROSS-COUNTRY SKIING AND NORDIC WALKING

The purpose of this study was to describe and validate a force transducer system specifically designed to measure the force exerted through the poles in cross-country skiing and Nordic walking. It is constituted by a custom built load cell and by a mounting system that allow to minimise cross talk effects. The system is applicable to standard carbon racing shafts to ensure the standard stiffness of the pole. The reliability of the system has been tested performing different static and dynamic tests. The comparison with the reference load cell has shown a good measurement linearity in the range of typical values for poling propulsion and a sensitivity only to the force axially applied to the shaft. The test performed on a 2D platform and with a motion capture system for the measurement of pole inclination, demonstrated the possibility to obtain a reliable measure of the vertical, longitudinal and lateral components of the force exerted by the subject. The accuracy, the portability of the system and their applicability to different shafts allow evaluation of poling action in both laboratory and field conditions, providing important information in cross-country skiing and Nordic walking biomechanical research

Independent, additive and interactive effects of acute normobaric hypoxia and cold on submaximal and maximal endurance exercise

Purpose: To evaluate the independent and combined effects of hypoxia (FiO2 = 13.5%) and cold (- 20 °C) on physiological and perceptual responses to endurance exercise. Methods: 14 trained male subjects ([Formula: see text]O2max: 64 ± 5 mL/kg/min) randomly performed a discontinuous maximal incremental test to exhaustion on a motorized treadmill under four environmental conditions: Normothermic-Normoxia (N), Normothermic-Hypoxia (H), Cold-Normoxia (C) and Cold-Hypoxia (CH). Performance and physiological and perceptual responses throughout exercise were evaluated. Results: Maximal WorkLoad (WL) and WL at lactate threshold (LT) were reduced in C (- 2.3% and - 3.5%) and H (- 18.0% and - 21.7%) compared to N, with no interactive (p = 0.25 and 0.81) but additive effect in CH (- 21.5% and - 24.6%). Similarly, HRmax and Vemax were reduced in C (- 3.2% and - 14.6%) and H (- 5.0% and - 7%), showing additive effects in CH (- 7.7% and - 16.6%). At LT, additive effect of C (- 2.8%) and H (- 3.8%) on HR reduction in CH (- 5.7%) was maintained, whereas an interactive effect (p = 0.007) of the two stressors combined was noted on Ve (C: - 3.1%, H: + 5.5%, CH: - 10.9%). [La] curve shifted on the left in CH, displaying an interaction effect between the 2 stressors on this parameter. Finally, RPE at LT was exclusively reduced by hypoxia (p < 0.001), whereas TSmax is synergistically reduced by cold and hypoxia (interaction p = 0.047). Conclusion: If compared to single stress exposure, exercise performance and physiological and perceptual variables undergo additive or synergistic effects when cold and hypoxia are combined. These results provide new insight into human physiological responses to extreme environments

On the residual opening of hydraulic fractures

Hydraulic stimulation technologies are widely applied across resource and power generation industries to increase the productivity of oil/gas or hot water reservoirs. These technologies utilise pressurised water, which is applied inside the well to initiate and drive fractures as well as to open a network of existing natural fractures. To prevent the opened fractures from complete closure during production stage, small particles (proppants) are normally injected with the pressurised fluid. These particles are subjected to confining stresses when the fluid pressure is removed, which leads to a partial closure of the stimulated fractures. The residual fracture openings are the main outcome of such hydraulic stimulations as these openings significantly affect the permeability of the reservoirs and, subsequently, the well productivity. Past research was largely focused on the assessment of conditions and characteristics of fluid driven fractures as well as proppant placement techniques. Surprisingly, not much work was devoted to the assessment of the residual fracture profiles. In this work we develop a simplified non-linear mathematical model of residual closure of a plane crack filled with deformable particles and subjected to a remote compressive stress. It is demonstrated that the closure profile is significantly influenced by the distribution and compressibility of the particles, which are often ignored in the current evaluations of well productivity. © 2013 Springer Science+Business Media Dordrecht.Luiz Bortolan Neto, Andrei Kotouso

Specific strength in sport climbing disciplines

Strength of the upper limbs has been suggested to de a determinant in climbing performance (1). However, different kinds of assessments have provided contradictory results. Strength has been measured with general (handgrip) and specific (SCD, specific climbing dynamometer) tools. Isometric maximal voluntary contraction (MVC) and rate of force development (RFD) can be considered as outcomes. The SCD showed validity (correlated with lead performance n=38, r=-0.61, p<0.001)(2), reliability (Typical Error as CV was 8, 16% for SCD MVC and peak-RFD and ICC of 0.91, 0.82, respectively) (3) and internal responsiveness (effect size 1.44 in SCD peak-RFD) (4). Lead and Boulder are widespread disciplines in sport climbing. Boulder climbers showed higher values of MVC and pRFD compared to Lead climbers (5). Muscle fatigue (i.e. decrease in MVC and RFD parameters) can give further details in the importance of neuromuscular properties in sport climbing disciplines. The aim of this study was to examine muscle fatigue after Boulder and Lead activity. Methods Fourteen climbers (age 29 \ub1 10 yrs, height 176 \ub1 8 cm, weight 70 \ub1 7 kg, climbing level IRCRA scale moderate to advanced) participated in a simulated competition in Lead and Boulder. Before the measurement climbers were involved in a survey investigation. Participants were randomly assigned to a sequence Lead-Boulder or Boulder-Lead in a counterbalanced design with two conditions (i.e. Lead and Boulder) and washout (i.e. recovery) period of 4 hours. Specific strength (MVC and RFD) was measured with a SCD at baseline and after Boulder and Lead. Results Climbers perceived strength of the forearms to be important in boulder and lead (12 and 13% of the answers) performances and physical strength of higher importance in boulder compared to lead (34 and 42% of answers). MVC and pRFD at baseline were 7.2 \ub1 1.1 N/kg and 38.2 \ub1 8.6 N/kg/s. After boulder, MVC and pRFD were 6.8 \ub1 1.5 N/kg and 32.7 \ub1 10.3 N/kg/s, percentage differences -7.4 (90% CI \ub1 7.3) and -16.3 (90% CI \ub1 15). After lead MVC and pRFD were 6.4 \ub1 1.7 N/kg and 30 \ub1 11.3 N/kg/s, percentage differences -12.8 (90% CI \ub1 10.8) and -25.4 (90% CI \ub1 13). Discussion The decline in strength after Lead and Boulder simulation of competition confirms the occurrence of muscle fatigue. This study confirmed previous results attained after a Lead official competition and simulation for pRFD (-19%) and MVC (-6%) (2). The great decline in pRFD underlined the importance of rapidly exerting the strength (i.e. contact strength) during both disciplines. Conclusion Specific strength should be assessed with SCD. Rate of force development seams to be more appropriate compared to maximal voluntary contraction for investigating fatigue after climbing disciplines. References 1. Watts, P.B., Eur J Appl Physiol, 2004. 91(4): 361-72. 2. Fanchini, M., et al. In 15th Annual Congress of ECSS. 2010. Antalya, Turkey 3. Fanchini M, et al. In 16th Annual Congress of Sport Science ECSS. 2011. Liverpool, UK. 4 Fanchini M, et al. In 2nd International Rock Climbing Research Congress 2014, Pontresina, Switzerland 5 Fanchini M et al. J Strength Cond Res,2013. 27(2): 310-31

Injury and Illness Rates During Ultratrail Running

This study aimed to describe injury/illness rates in ultratrail runners competing in a 65-km race to build a foundation for injury prevention and help race organizers to plan medical provision for these events. Prospectively transcribed medical records were analysed for 77 athletes at the end of the race. Number of injuries/illnesses per 1\u2009000 runners and per 1\u2009000-h run, overall injury/illness rate and 90% confidence intervals and rates for major and minor illnesses, musculoskeletal injuries, and skin disorders were analysed. A total of 132 injuries/illnesses were encountered during the race. The overall injuries/illnesses were 1.9 per runner and 13.1 per 1\u2009000-h run. Medical illnesses were the most prominent medical diagnoses encountered (50.3%), followed by musculoskeletal injuries (32.8%), and skin-related disorders (16.9%). Despite the ultra-long nature of the race, the majority of injuries/illnesses were minor in nature. Medical staff and runners should prepare to treat all types of injuries and illnesses, especially the fatigue arising throughout the course of an ultratrail run and injuries to the lower limbs. Future studies should attempt to systematically identify injury locations and mechanisms in order to better direct injury prevention strategies and plan more accurate medical care

Detecting early signals of COVID-19 outbreaks in 2020 in small areas by monitoring healthcare utilisation databases: first lessons learned from the Italian Alert_CoV project

During the COVID-19 pandemic, large-scale diagnostic testing and contact tracing have proven insufficient to promptly monitor the spread of infections.AimTo develop and retrospectively evaluate a system identifying aberrations in the use of selected healthcare services to timely detect COVID-19 outbreaks in small areas. Methods: Data were retrieved from the healthcare utilisation (HCU) databases of the Lombardy Region, Italy. We identified eight services suggesting a respiratory infection (syndromic proxies). Count time series reporting the weekly occurrence of each proxy from 2015 to 2020 were generated considering small administrative areas (i.e. census units of Cremona and Mantua provinces). The ability to uncover aberrations during 2020 was tested for two algorithms: the improved Farrington algorithm and the generalised likelihood ratio-based procedure for negative binomial counts. To evaluate these algorithms' performance in detecting outbreaks earlier than the standard surveillance, confirmed outbreaks, defined according to the weekly number of confirmed COVID-19 cases, were used as reference. Performances were assessed separately for the first and second semester of the year. Proxies positively impacting performance were identified. Results: We estimated that 70% of outbreaks could be detected early using the proposed approach, with a corresponding false positive rate of ca 20%. Performance did not substantially differ either between algorithms or semesters. The best proxies included emergency calls for respiratory or infectious disease causes and emergency room visits. Conclusion: Implementing HCU-based monitoring systems in small areas deserves further investigations as it could facilitate the containment of COVID-19 and other unknown infectious diseases in the future