Density distribution of particles upon jamming after an avalanche in a 2D silo

We present a complete analysis of the density distribution of particles in a two dimensional silo after discharge. Simulations through a pseudo-dynamic algorithm are performed for filling and subsequent discharge of a plane silo. Particles are monosized hard disks deposited in the container and subjected to a tapping process for compaction. Then, a hole of a given size is open at the bottom of the silo and the discharge is triggered. After a clogging at the opening is produced, and equilibrium is restored, the final distribution of the remaining particles at the silo is analyzed by dividing the space into cells with different geometrical arrangements to visualize the way in which the density depression near the opening is propagated throughout the system. The different behavior as a function of the compaction degree is discussed.Comment: 11 pages, 10 figure

Experimental characterizatin of axial dispersion in coiled flow inverters

Narrow residence time distributions (RTDs) are extremely desirable in many chemical engineering processes where plug flow behaviour is requested. However, at low Reynolds numbers the flow is laminar resulting in strong radial velocity gradients. This in turn causes spreading of fluid particles, usually referred to as hydrodynamic dispersion. Such problem is particularly relevant to microfluidic devices operated in laminar regime due to the reduced dimension and low operating flow rates. Many solutions have been proposed to reduce the hydrodynamic dispersion: static mixers, segmented flow, secondary flow, etc. The latter relies on the action of centrifugal force inducing transversal mixing in helically coiled tubes. Further mixing and therefore reduced dispersion can be achieved by introducing geometrical disturbances, generating chaotic advection. Coiled flow inverters (CFI) exploit the beneficial effects of secondary flow and chaotic advection. They consist of sections of helically coiled tubes with 90-degree bends placed at regular intervals along a cylindrical support. Despite being a very promising solution, they have not been extensively adopted. This is due to the lack of experimental data and correlations relating the design parameters and operating conditions to the reduction of hydrodynamic dispersion. In this thesis, a flexible and reliable experimental procedure was developed to investigate RTD in microfluidic devices. It resorts to step input injections and UV-vis inline spectroscopy for detecting the concentration of tracer. The procedure was validated using Taylor’s dispersion for straight tubes. The platform was then employed to perform experiments on CFIs, constructed with microfluidic capillaries, varying operating conditions and a geometrical parameter. A similar characterization was carried out on helically coiled tubes. A significant reduction of axial dispersion was observed as compared to straight pipes, confirming the available data in the literature. It was also demonstrated that the curvature ratio primarily defines the strength of radial mixing in CFIs and therefore represents a crucial design parameter

Chronicle of a death foretold. It is time for echocardiographic screening in young athletes

Background: The novel "Chronicle of a death foretold" by Gabriel Garcia Marquez is a story of a sudden death which could have been prevented. In 1976, within the University of Maryland basketball program and only 8 weeks apart, two athletes died suddenly during physical exertion. They were affected by hypertrophic cardiomyopathy and Marfan syndrome and in both cases an echocardiogram would have prevented the tragic epilogue. This coincidence drew everyone's attention and experts' interest on sudden death in sports.Methods and results: Even in recent Italian history, unexpected deaths continue to affect athletes but surprisingly any real knowledge regarding the numbers and the impact of those tragedies must take medical literature and non-medical press into consideration. Herein we report the clinical case of a 13-year-old patient with a bicuspid aortic valve, whose mother was alarmed by the news of a young boy who died because of an anomalous origin of coronary artery (AOCA) which had not been diagnosed at transthoracic echocardiography (TTE). Her obstinacy induced the physicians to repeat TTE and led to the same diagnosis in her son: actually, his right coronary artery originated from the opposite sinus of Valsalva. The suspicion was confirmed by coronary CT scan and, thanks to appropriate therapy, the boy now fares well.Conclusions: AOCA is the second most common cause of sudden death in young athletes. Although AOCA is often undetectable at ECG, TTE increases sensitivity of preparticipation screening. It could therefore allow us to avoid such coincidences and prevent sudden juvenile death

Apoptotic cell death in canine hair follicle

Apoptotic cell death is an essential homeostatic mechanism involved in the control of cellular turnover in a variety of adult tissues. Cytoplasmic and nuclear condensation morphologically define this process whose biochemical hallmark is extensive DNA fragmentation into discrete oligonucleosomic units. Hair follicle growth and regression has been shown to be correlated with apoptosis in humans, mice, rats and guinea pigs. The present study was carried out to evaluate its implication in canine hair biology in order to define the spatio-temporal relationship between apoptosis and the hair cycle in dogs. As assessed by terminal deoxy-nucleotidyl transferase-mediated d-UTP nick-end-labelling (TUNEL) and by basic histological and ultrastructural assays, apoptotic cells appeared both in the growing and in the regressing follicle epithelium showing the well characterized morphological features described in the previous relevant literature

Development of interconnected silicon micro-evaporators for the on-detector electronics cooling of the future ITS detector in the ALICE experiment at LHC

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The design of the future High Energy Physics (HEP) particle detectors for the upgrade of the LHC (Large Hadron Collider) experiments at CERN (European Organization for Nuclear Research) is pushing technological frontiers to the limit trying to reach unprecedented accuracy in particles identification and particle production dynamics in ultra-relativistic hadron collisions. The thermal management of the on-detector electronics and the development of low mass integrated cooling systems have become a crucial task in the design of silicon tracking detectors for HEP applications. In this paper, we present a novel concept of low mass interconnected silicon microchannel devices for the future Inner Tracking System of the ALICE (A Large Ion Collider Experiment) detector at LHC. This innovative design achieves the requirements of the detector while minimizing the total material budget

Expression of mesenchymal stem cell marker CD90 on dermal sheath cells of the anagen hair follicle in canine species

The dermal sheath (DS) of the hair follicle is comprised by fibroblast-like cells and extends along the follicular epithelium, from the bulb up to the infundibulum. From this structure, cells with stem characteristics were isolated: they have a mesenchymal origin and express CD90 protein, a typical marker of mesenchymal stem cells. It is not yet really clear in which region of hair follicle these cells are located but some experimental evidence suggests that dermal stem cells are localized prevalently in the lower part of the anagen hair follicle

Transient Effects of Snow Cover Duration on Primary Growth and Leaf Traits in a Tundra Shrub

With the recent climate warming, tundra ecotones are facing a progressive acceleration of spring snowpack melting and extension of the growing season, with evident consequences to vegetation. Along with summer temperature, winter precipitation has been recently recognised as a crucial factor for tundra shrub growth and physiology. However, gaps of knowledge still exist on long-living plant responses to different snowpack duration, especially on how intra-specific and year-to-year variability together with multiple functional trait adjustments could influence the long-term responses. To fill this gap, we conducted a 3 years snow manipulation experiment above the Alpine treeline on the typical tundra species Juniperus communis, the conifer with the widest distributional range in the north emisphere. We tested shoot elongation, leaf area, stomatal density, leaf dry weight and leaf non-structural carbohydrate content of plants subjected to anticipated, natural and postponed snowpack duration. Anticipated snowpack melting enhanced new shoot elongation and increased stomatal density. However, plants under prolonged snow cover seemed to compensate for the shorter growing period, likely increasing carbon allocation to growth. In fact, these latter showed larger needles and low starch content at the beginning of the growing season. Variability between treatments slightly decreased over time, suggesting a progressive acclimation of juniper to new conditions. In the context of future warming scenarios, our results support the hypothesis of shrub biomass increase within the tundra biome. Yet, the picture is still far from being complete and further research should focus on transient and fading effects of changing conditions in the long term