Erasure Tolerant Quantum Memory and the Quantum Null Energy Condition in Holographic Systems.

Investigating principles for storage of quantum information at finite temperature with minimal need for active error correction is an active area of research. We bear upon this question in two-dimensional holographic conformal field theories via the quantum null energy condition that we have shown earlier to implement the restrictions imposed by quantum thermodynamics on such many-body systems. We study an explicit encoding of a logical qubit into two similar chirally propagating excitations of finite von Neumann entropy on a finite temperature background whose erasure can be implemented by an appropriate inhomogeneous and instantaneous energy-momentum inflow from an infinite energy memoryless bath due to which the system transits to a thermal state. Holographically, these fast erasure processes can be depicted by generalized AdS-Vaidya geometries described previously in which no assumption of specific form of bulk matter is needed. We show that the quantum null energy condition gives analytic results for the minimal finite temperature needed for the deletion which is larger than the initial background temperature in consistency with Landauer's principle. In particular, we find a simple expression for the minimum final temperature needed for the erasure of a large number of encoding qubits. We also find that if the encoding qubits are localized over an interval shorter than a specific localization length, then the fast erasure process is impossible, and furthermore this localization length is the largest for an optimal amount of encoding qubits determined by the central charge. We estimate the optimal encoding qubits for realistic protection against fast erasure. We discuss possible generalizations of our study for novel constructions of fault-tolerant quantum gates operating at finite temperature.

Quantum Thermodynamics of Holographic Quenches and Bounds on the Growth of Entanglement from the Quantum Null Energy Condition.

The quantum null energy condition (QNEC) is a lower bound on the energy-momentum tensor in terms of the variation of the entanglement entropy of a subregion along a null direction. To gain insights into quantum thermodynamics of many-body systems, we study if the QNEC restricts irreversible entropy production in quenches driven by energy-momentum inflow from an infinite memoryless bath in two-dimensional holographic theories. We find that an increase in both entropy and temperature, as implied by the Clausius inequality of classical thermodynamics, is necessary but not sufficient to not violate QNEC in quenches leading to transitions between thermal states with momentums that are dual to Banados-Teitelboim-Zanelli geometries. For an arbitrary initial state, we can determine the lower and upper bounds on the increase of entropy (temperature) for a fixed increase in temperature (entropy). Our results provide explicit instances of quantum lower and upper bounds on irreversible entropy production whose existence has been established in literature. We also find monotonic behavior of the nonsaturation of the QNEC with time after a quench, and analytically determine their asymptotic values. Our study shows that the entanglement entropy of an interval of length l always thermalizes in time l/2 with an exponent 3/2. Furthermore, we determine the coefficient of initial quadratic growth of entanglement analytically for any l, and show that the slope of the asymptotic ballistic growth of entanglement for a semi-infinite interval is twice the difference of the entropy densities of the final and initial states. We determine explicit upper and lower bounds on these rates of growth of entanglement.

Sliding wear and friction characteristics of polymer nanocomposite PAEK-PDMS with nano-hydroxyapatite and nano-carbon fibres as fillers.

The development of a suitable polymeric bioactive composite with hydroxyapatite as a filler is one of the very actively pursued areas in bioapplications. This report concerns development of such a novel polymeric biocomposite viz. poly (aryl ether) ketone-poly (dimethylsiloxane) with a small percentage of nano carbon fibres and varying percentages of nanohydroxyapatite particulates as fillers. The earlier characterization of this material involving mechanical, thermal and bio-compatibility studies showed optimum improved behaviour at about 7% nanohydroxyapatite loading as reported elsewhere. In this study, the wear and friction response of this biocomposite was tested in air under dry sliding conditions against hard steel using a pin-on-disc apparatus. Interestingly, the adhesive wear characteristics of this nanocomposite with varying nanohydroxyapatite percentages showed a trend similar to that in other characteristics with lowest wear occurring around the same nanohydroxyapatite percentage. It was observed that the specific wear rate in this novel nanocomposite was exceptionally low [~ 10-8 (mm3/N-m)] compared to that in other similar polymer composites. The origin of this very low wear rate can be associated with the multiple strategies used in the preparation of this nanocomposite such as the use of poly (dimethylsiloxane) which is known to provide a cushioning effect in the matrix. In addition, the phosphate grafting of poly (dimethylsiloxane), the nanonature of both the fillers and their specific surface treatments using aminosilane for enhancing the matrix- filler interfacial bonding all of them seem to have played their expected beneficial roles resulting in the above very low wear rate. The earlier studies on this nanocomposite have shown improvement of the mechanical compressive strength with the addition of carbon nanofibres. Interestingly, here the friction coefficient of the nanocomposite with carbon nanofibres is consistently higher than that without carbon nano fibres for different nanohydroxyapatite percentages samples, for both low (5 N) as well as high (30 N) applied load. It could possibly be due to dislodged carbon nano fibres acting as a third body abrasive or fibres acting as weak links in the matrix filler network affecting the friction response. These wear and friction measurements have clearly brought out the various interesting aspects of the tribological response of the nanocomposite material and the intricate roles played by its matrix component poly (dimethylsiloxane) and the surface treated nano fillers nanohydroxyapatite and nano carbon fibre.

Synthesis and swelling characteristics of chitosan and CMC grafted sodium acrylate-co-acrylamide using modified nanoclay and examining its efficacy for removal of dyes.

Chitosan/carboxy methyl chitosan (CMC) grafted sodium acrylate-co-acrylamide/nanoclay superabsorbent nanocomposites have been synthesized in this study by following conventional and microwave assisted grafting methods. Microwave assisted grafting method showed higher grafting yield with enhanced reaction rate. Effect of nanoclay on water adsorption and swelling behaviour of both the composites in acidic, neutral and alkaline medium has been studied. Results showed enhanced swelling rate and water adsorption of both composites after adding 5% of silane treated nanoclay. Dye adsorption capacity of both the composites has been investigated for crystal violet, napthol green and sunset yellow dyes. It was observed that addition of 5% nanoclay enhanced the dye adsorption in both the composites. Langmuir and Freundlich isotherm models have been used to explain the dye adsorption capabilities. The chitosan and CMC nanocomposites follow both the models with R2 value more than 0.97. Both the composites showed enhanced dye adsorption with 5% nanoclay. Effect of pH on dye adsorption has also been studied in both the composites. Chitosan nanocomposites showed better performance in dye removal as compared to CMC nanocomposites.

Mechanical, thermal and bio-compatibility studies of PAEK-hydroxyapatite nanocomposites.

In this study high performance bone analogue has been developed using poly(aryl ether) ketone, poly(dimethyl siloxane) and reinforced with nanohydroxyapatite as biocompatible filler. Compressive, tensile and flexural properties have shown sustained improvement up to 7% of nanohydroxyapatite loading. The mechanical properties were further analyzed using micromechanical theories for good interfacial adhesion between matrix and filler. The composites are cytocompatible and revealed multiple layers of apatite formation in simulated body fluid. The thickness of apatite layer increased with increase in nanohydroxyapatite loading in the composite. Poly(dimethyl siloxane) has been grafted with phosphate group to enhance compatibility with nanohydroxyapatite. Nanohydroxyapatite has been treated with silane to enhance compatibility and facilitate dispersion in the matrix as observed through transmission electron microscopy, scanning electron microscopy and X-Ray diffraction studies.

Chitosan-nanohydroxyapatite composites: mechanical, thermal and bio-compatibility studies.

Bionanocomposites of chitosan were prepared with nanohydroxyapatite (nHA) using 2-hydroxyethyl methacrylate (HEMA) as coupling agent. The tensile and flexural properties for 8% nHA loading showed optimal values. Compressive modulus also considerably increased from 525.16 MPa (0% nHA) to 1326.5 MPa with 10% nHA. Surface functionalization of fillers along with the addition of HEMA as coupling agent led to enhanced mechanical properties similar to human bone. The mechanical properties were further analyzed using micromechanical theories which indicated good interfacial adhesion between the matrix and fillers. The composites showed cytocompatibility. Multiple layers of apatite formation have been observed when the nanocomposites were soaked in simulated body fluid (SBF). Hence, these composites showed potential for bone substitute applications.

An evidence based strategy for follow up after breast conserving treatment for breast cancer.

BACKGROUND AND OBJECTIVES: Follow up for breast cancer patients aims at the timely detection of loco-regional recurrences and contralateral breast cancers (LRR). This study investigates the annual risk of LRR after breast conserving treatment (BCT) and the potential value of mammographic surveillance and/or routine clinical examination. METHODS: Data on 650 women who underwent BCT were obtained and LRR was divided into parenchymal and non-parenchymal. LRR-free and cumulative LRR-free rates were calculated. In patients where recurrence was diagnosed at a routine clinic visit and had negative mammography ("clinical detection only" group) were also separately examined. RESULTS: Median follow up was 115 months, range 9-196. Seventy-three patients had parenchymal and 16 nodal recurrence. The median probability of LRR was 1.4% and of parenchymal LRR was 1.32% per year, remaining constant for up to 168 months. The 16 patients in the "clinical detection only" group relapsed mainly during the first 2 years (annual risk 0.77% and 0.80%, respectively). CONCLUSIONS: This study shows that the risk of parenchymal LRR remains constant for at least 14 years and is significant enough to warrant routine long-term follow up mammography. Routine clinical examination contributes significantly to the detection of LRR only for the first 2 years.

Be careful what you wish for: an ingested foreign body masquerading as cancer.

We present a case in which a patient with suspected colorectal cancer, referred to the surgical outpatient clinic, was subsequently found to have a chicken wishbone apparently perforating the sigmoid colon. This demonstrates the complexities of diagnosis and management of an unusual presentation of ingested foreign body. This case is a useful learning point in consideration of differential diagnosis in the presentation of an apparently malignant lesion.

Intervention-free interval following strictureplasty for Crohn's Disease.

INTRODUCTION: Strictureplasty is now well established as a bowel-sparing alternative for surgical treatment of complicated Crohn's disease. Limited resection is still preferred in patients with uncomplicated disease, as subsequent reoperation rates are low. METHODS: A retrospective review of 26 patients who underwent surgery for small bowel Crohn's disease between 1996 and 2004 was undertaken. A total of 96 small bowel strictureplasties had been performed; 19 patients had strictureplasties performed in isolation, and the remaining 7 patients underwent strictureplasty with concomitant limited resection. RESULTS: There was no operative mortality. The median follow-up was 41 months. Four patients developed complications that required further surgery. At 41 months, 73.3% of patients undergoing strictureplasty alone and 79.7% undergoing strictureplasty with concomitant resection were intervention-free. If followed up to 70 months or more, the same proportion of patients would remain intervention-free. Four patients developed further recrudescent disease and required surgery: strictureplasty, limited resection, or both. Of these patients, 25% were intervention-free at 41 months. CONCLUSIONS: Our results show that strictureplasty alone or with concomitant resection can confer intervention-free periods of 41 months or more in 73.3% of patients, suggesting that strictureplasty can be utilized as an alternative to limited resection in uncomplicated Crohn's disease.

Strictureplasty for active Crohn's disease.

BACKGROUND AND AIMS: Several studies over the last 20 years have confirmed the safety and efficacy of strictureplasty in the treatment of obstructive Crohn's disease. However, almost all of these studies use strictureplasty to treat fibrotic strictures: limited resection being preferred to treat active disease strictures. One study dating from 1986 used strictureplasty to treat purely active disease strictures, with disappointing results. No other similar studies have been published. We investigate the complication and recrudescence rates together with the intervention-free intervals in patients undergoing strictureplasty for active disease strictures. METHODS: A retrospective review of 14 patients who underwent strictureplasty either in isolation or in combination with limited resection for active small bowel Crohn's disease between 1996 and 2004 was undertaken. RESULTS: A total of 73 strictureplasties were carried out. There was no operative mortality; however, one patient subsequently died from metastatic small bowel adenocarcinoma arising from existing Crohn's disease. One patient subsequently developed complications directly attributed to strictureplasty and required further surgery. Three patients developed recrudescent disease and required further surgery in the form of either strictureplasty, limited resection or both. All patients undergoing strictureplasty with resection and over 70% of patients undergoing strictureplasty alone were intervention-free at 41 months. With extended follow-up, the same proportion of patients would remain intervention-free at 70 months or longer. CONCLUSIONS: The use of strictureplasty in active disease strictures is well tolerated and has similar, if not better, recurrence and complication rates when compared with limited resection in patients with similar disease profiles.

Intra-abdominal metastases from soft tissue sarcoma.

OBJECTIVE: To define the clinical features and prognosis of patients with abdominal metastasis from primary soft tissue sarcoma (STS) at other sites. METHODS: All patients with abdominal metastasis from STS were identified from the Royal Marsden Hospital Sarcoma Unit prospective database from January 1990 to July 2001. RESULTS: Nineteen patients developed abdominal metastasis out of a cohort of 2127 patients (0.9%) evaluated during the study interval. The median age was 49 (19-71) years. The median time to abdominal metastasis from diagnosis of the primary was 27 (8-91) months. The presenting complaints were incomplete intestinal obstruction (n = 5), abdominal pain (n = 4), mass (n = 2), gastrointestinal bleed (n = 2), urinary obstruction (n = 2), anorexia (n = 1), and abdominal distension (n = 1). Emergency laparotomy was done for perforative peritonitis (n = 2), intussusception (n = 2), and bleed in spleen (n = 1). Two patients were asymptomatic. The common histologies were myxoid liposarcoma (n = 6) and leiomyosarcoma (n = 4). The median follow-up of survivors post metastasis was 12 months. Abdominal metastatectomy was performed in 16 patients, 3 of these patients had abdominal recurrences. The 1- and 2-year overall disease specific survival for the 19 patients was 66% (SE = 11%) and 43% (SE = 13%) with a median survival of 13 months (95% CI = 11.8-14.7). Metastasectomy was associated with slight improved median post-metastasis survival (33 months vs. 8 months for unresected patients). CONCLUSIONS: Although abdominal metastasis is rare, vigilance is warranted. Symptomatic patients should be examined and investigated thoroughly for metastases. Surgery is the treatment of choice for patients with an acute presentation; however, survival is dismal.

Cauda equina compression after trauma: an unusual presentation of spinal epidural lipoma.

STUDY DESIGN: A case report is presented. OBJECTIVE: To describe a case of a spinal epidural lipoma presenting as a cauda equina compression syndrome secondary to trauma. SUMMARY OF BACKGROUND DATA: Epidural lipomas are rare lesions that present as back pain with progressive neurologic symptoms. METHODS: A patient presenting with cauda equina compression after an injury was investigated and treated surgically. The clinical follow-up period was 3 years. RESULTS: Imaging of the lumbar spine showed an extradural mass compressing the cauda equina. The patient underwent emergency surgery, and an adipose mass was removed. Neurologic recovery was observed and maintained 3 years after surgery. CONCLUSIONS: Previously asymptomatic epidural masses such as lipomas can present with neurologic deficit after trauma. Appropriate imaging can help in the diagnosis and management of such cases.