Dynamical facilitation governs glassy dynamics in suspensions of colloidal ellipsoids

One of the greatest challenges in contemporary condensed matter physics is to ascertain whether the formation of glasses from liquids is fundamentally thermodynamic or dynamic in origin. Although the thermodynamic paradigm has dominated theoretical research for decades, the purely kinetic perspective of the dynamical facilitation (DF) theory has attained prominence in recent times. In particular, recent experiments and simulations have highlighted the importance of facilitation using simple model systems composed of spherical particles. However, an overwhelming majority of liquids possess anisotropy in particle shape and interactions, and it is therefore imperative to examine facilitation in complex glass formers. Here, we apply the DF theory to systems with orientational degrees of freedom as well as anisotropic attractive interactions. By analyzing data from experiments on colloidal ellipsoids, we show that facilitation plays a pivotal role in translational as well as orientational relaxation. Furthermore, we demonstrate that the introduction of attractive interactions leads to spatial decoupling of translational and rotational facilitation, which subsequently results in the decoupling of dynamical heterogeneities. Most strikingly, the DF theory can predict the existence of reentrant glass transitions based on the statistics of localized dynamical events, called excitations, whose duration is substantially smaller than the structural relaxation time. Our findings pave the way for systematically testing the DF approach in complex glass formers and also establish the significance of facilitation in governing structural relaxation in supercooled liquids.The transformation of liquids into glasses is as ubiquitous as it is enigmatic. From the formation of obsidian during volcanic eruptions (1) and fabrication of superstrong metallic glasses (2) to exotic forms of slow dynamics in crystals of colloidal dimers (3) and Janus particles (4), glass formation pervades nature, industry, and academia. A vast majority of molecular glass-forming materials exhibit anisotropy in shape and interparticle interactions, which often has a profound influence on their glassy dynamics. The rapidly expanding repertoire of chemists has made it possible to design colloidal particles of desired shape and interactions that can serve as realistic experimental analogs of these molecular liquids (5). By contrast, prominent theories like the Adam–Gibbs (6) theory, random first-order transition (RFOT) theory (7, 8), and the dynamical facilitation (DF) theory (9, 10) have been tested predominantly on spherical glass formers with isotropic interactions, which exhibit gross features of glassy dynamics, but fail to capture the nuances of vitrification in complex systems.The discovery of growing static (11–16) and dynamic (17–21) length scales appears to support the thermodynamic perspective of the Adam–Gibbs and RFOT theories. However, the growth in static length scales over the dynamical range accessible to numerical simulations is often minuscule and much smaller than the corresponding growth in dynamic length scales (21, 22). This renders any causal connection between growing static length scales and growing timescales doubtful (22). Moreover, recent simulations (23) and colloid experiments (24) have shown that growing dynamical correlations in the form of string-like cooperative motion emerge naturally within the purely kinetic approach of the DF theory. To compound matters further, facilitation is present even within the RFOT framework, albeit as a consequence of slow dynamics rather than a cause (25). Thus, although DF has been shown to exist (23, 24, 26–29), its relative importance as a mechanism of structural relaxation is still debated (30–32). The application of the DF approach to complex glass formers will therefore not only enhance our understanding of glass transitions in these systems, but also help ascertain the relevance of facilitation in governing structural relaxation.Here, we apply the DF theory to elucidate glass formation in suspensions of colloidal ellipsoids with repulsive as well as attractive interactions. The DF theory claims that structural relaxation in glass-forming liquids proceeds via a process known as dynamical facilitation, whereby localized mobile regions, termed excitations, mediate motion in neighboring regions in a manner that conserves mobility (9, 10). We first show that the notions of localized excitations and facilitated dynamics can be extended even to orientational relaxation. Next, we demonstrate that the spatial decoupling of dynamical heterogeneities (DHs) observed in colloid experiments stems from the spatial decoupling of rotational and translational facilitation. Most importantly, the DF theory can predict the existence of recently observed reentrant glass transitions (33) from the density dependence of the concentration of excitations. Our findings not only highlight the importance of facilitated dynamics in anisotropic glass formers but also reinforce the claim that, in the broader context of the glass transition, facilitation dominates structural relaxation.     

The Outcome of Modified Extended Trochanteric Osteotomy in Revision THA for Vancouver B2/B3 Periprosthetic Fractures of the Femur

We hypothesised that a modified ETO in patients undergoing revision total hip arthroplasty (THA) for treatment of Vancouver B2/B3 peri-prosthetic fractures would be associated with good clinical outcomes. A retrospective review was conducted of 34 patients (mean age 73 years). At mean follow-up of 57 months, the ETO had healed in all patients. Two patients had subsidence of the femoral stem at two and three years postoperatively requiring revision, and one patient had a dislocation 3 months after surgery. The mean Harris Hip Score at the time of the final follow-up was 76.9 (range, 46–95); 23/34 patients had an excellent result, 7/34 a good result, and 4/34 a poor result. We conclude that satisfactory outcomes can be obtained using this technique.     

Single-stage earlobe reconstruction: a simple method with promising results

Various methods have been described in the literature for earlobe reconstruction in one or many stages. Authors describe here a simple, single-stage technique to reconstruct the loss of the earlobe. The technique is clearly illustrated in a step-by-step manner and produces a natural-looking earlobe without an unpleasant secondary deformity with desirable texture and color match. Level of Evidence: Level IV, therapeutic study.     

A curious case of foreign body induced jejunal obstruction and perforation

INTRODUCTION

Accidental and unnoticed ingestion of foreign bodies are not very uncommon. Most of such foreign bodies pass through gastrointestinal tract uneventfully and only on rare instances cause obstruction and/or perforation.

PRESENTATION OF CASE

We are reporting a case in which a 45 yr old male presented to accident and emergency department of our institute with complaints of pain abdomen, greenish vomiting, abdominal distension, fever and non passage of flatus and stool following alcoholic binge 15 days back. On presentation tachycardia, hypotension, generalised abdominal tenderness and guarding were present. After initial resuscitation and investigation diagnosis of perforation peritonitis was made and emergency exploratory lapratomy was done and a single perforation with plastic foreign body protruding through it was found in jejunum 5 cm distal to duodeno-jejunal junction.

DISCUSSION

The majority of ingested FBs that reach the stomach pass uneventfully through the gastrointestinal tract. The majority of cases occur in children. Only 1% of patient of patients requires surgical intervention depending upon nature, size and shape of the foreign body.

CONCLUSION

Present case report intends to draw the attention towards possibility of intestinal obstruction and perforation by a single plastic foreign body. High index of suspicion is needed as this foreign body is not even radio-opaque and cannot be picked up in X-ray investigations. Also with increasing use of such plastic materials there are increased chances of such incidents.     

Volvulus of ileal S-pouch: A rare complication of ileal pouch anal anastomoses

INTRODUCTION

Ileal pouch anal anastomosis (IPAA) after total proctocolectomy is a frequently performed surgery for medically refractory ulcerative colitis (UC). Volvulus of the ileal pouch as a complication of IPAA is extremely rare. We present a case of volvulus of S-type ileal pouch.

PRESENTATION OF CASE

A 28 year old male, with history of total proctocolectomy with IPAA for severe UC in 2009 presented with signs of bowel obstruction. Emergency laparotomy was done and a volvulus of the S-type ileal pouch was derotated and pouchpexy done.

DISCUSSION

The IPAA has a wide spectrum of complications, with obstruction of proximal small bowel occurring frequently. Volvulus of the ileal pouch is extremely rare with only 3 reported cases. Early diagnosis and intervention is important to salvage the pouch. Computed tomography (CT) may aid the diagnosis in stable patients.

CONCLUSION

The diagnosis of ileal pouch volvulus although rare, should be kept in mind when dealing with patients complaining of recurrent obstruction following IPAA.