Valence Bonds in Random Quantum Magnets: Theory and Application to YbMgGaO4

We analyze the effect of quenched disorder on spin-1/2 quantum magnets in which magnetic frustration promotes the formation of local singlets. Our results include a theory for 2d valence-bond solids subject to weak bond randomness, as well as extensions to stronger disorder regimes where we make connections with quantum spin liquids. We find, on various lattices, that the destruction of a valence-bond solid phase by weak quenched disorder leads inevitably to the nucleation of topological defects carrying spin-1/2 moments. This renormalizes the lattice into a strongly random spin network with interesting low-energy excitations. Similarly when short-ranged valence bonds would be pinned by stronger disorder, we find that this putative glass is unstable to defects that carry spin-1/2 magnetic moments, and whose residual interactions decide the ultimate low energy fate. Motivated by these results we conjecture Lieb-Schultz-Mattis-like restrictions on ground states for disordered magnets with spin-1/2 per statistical unit cell. These conjectures are supported by an argument for 1d spin chains. We apply insights from this study to the phenomenology of YbMgGaO$_4$, a recently discovered triangular lattice spin-1/2 insulator which was proposed to be a quantum spin liquid. We instead explore a description based on the present theory. Experimental signatures, including unusual specific heat, thermal conductivity, and dynamical structure factor, and their behavior in a magnetic field, are predicted from the theory, and compare favorably with existing measurements on YbMgGaO$_4$ and related materials.Comment: v2: Stylistic revisions to improve clarity. 22 pages, 8 figures, 2 tables main text; 13 pages, 3 figures appendice

Simultaneous colorectal and hepatic procedures for colorectal cancer result in increased morbidity but equivalent mortality compared with colorectal or hepatic procedures alone: outcomes from the National Surgical Quality Improvement Program

AbstractBackgroundSimultaneous colorectal and hepatic surgery for colorectal cancer (CRC) is increasing as surgery becomes safer and less invasive. There is controversy regarding the morbidity associated with simultaneous, compared with separate or staged, resections.MethodsData for 2005–2008 from the National Surgical Quality Improvement Program (NSQIP) were used to compare morbidity after 19 925 colorectal procedures for CRC (CR group), 2295 hepatic resections for metastatic CRC (HEP group), and 314 simultaneous colorectal and hepatic resections (SIM group).ResultsAn increasing number of simultaneous resections were performed per year. Fewer major colorectal and liver resections were performed in the SIM than in the CR and HEP groups. Patients in the SIM group had a longer operative time and postoperative length of stay compared with those in either the CR or HEP groups. Simultaneous procedures resulted in higher rates of postoperative morbidity and major morbidity than CR procedures, but not HEP procedures. This difference was driven by higher rates of wound and organ space infections, and a greater incidence of septic shock. Mortality rates did not differ among the groups.ConclusionsHospitals in the NSQIP are performing more simultaneous colonic and hepatic resections for CRC. These procedures are associated with increases in operative time, length of stay and rate of perioperative complications. Simultaneous procedures do not, however, increase perioperative mortality

A new spin-anisotropic harmonic honeycomb iridate

The physics of Mott insulators underlies diverse phenomena ranging from high temperature superconductivity to exotic magnetism. Although both the electron spin and the structure of the local orbitals play a key role in this physics, in most systems these are connected only indirectly --- via the Pauli exclusion principle and the Coulomb interaction. Iridium-based oxides (iridates) open a further dimension to this problem by introducing strong spin-orbit interactions, such that the Mott physics has a strong orbital character. In the layered honeycomb iridates this is thought to generate highly spin-anisotropic interactions, coupling the spin orientation to a given spatial direction of exchange and leading to strongly frustrated magnetism. The potential for new physics emerging from such interactions has driven much scientific excitement, most recently in the search for a new quantum spin liquid, first discussed by Kitaev \cite{kitaev_anyons_2006}. Here we report a new iridate structure that has the same local connectivity as the layered honeycomb, but in a three-dimensional framework. The temperature dependence of the magnetic susceptibility exhibits a striking reordering of the magnetic anisotropy, giving evidence for highly spin-anisotropic exchange interactions. Furthermore, the basic structural units of this material suggest the possibility of a new family of structures, the `harmonic honeycomb' iridates. This compound thus provides a unique and exciting glimpse into the physics of a new class of strongly spin-orbit coupled Mott insulators.Comment: 12 pages including bibliography, 5 figure

Death-associated protein kinase 1 has a critical role in aberrant tau protein regulation and function

The presence of tangles composed of phosphorylated tau is one of the neuropathological hallmarks of Alzheimer's disease (AD). Tau, a microtubule (MT)-associated protein, accumulates in AD potentially as a result of posttranslational modifications, such as hyperphosphorylation and conformational changes. However, it has not been fully understood how tau accumulation and phosphorylation are deregulated. In the present study, we identified a novel role of death-associated protein kinase 1 (DAPK1) in the regulation of the tau protein. We found that hippocampal DAPK1 expression is markedly increased in the brains of AD patients compared with age-matched normal subjects. DAPK1 overexpression increased tau protein stability and phosphorylation at multiple AD-related sites. In contrast, inhibition of DAPK1 by overexpression of a DAPK1 kinase-deficient mutant or by genetic knockout significantly decreased tau protein stability and abolished its phosphorylation in cell cultures and in mice. Mechanistically, DAPK1-enhanced tau protein stability was mediated by Ser71 phosphorylation of Pin1, a prolyl isomerase known to regulate tau protein stability, phosphorylation, and tau-related pathologies. In addition, inhibition of DAPK1 kinase activity significantly increased the assembly of MTs and accelerated nerve growth factor-mediated neurite outgrowth. Given that DAPK1 has been genetically linked to late onset AD, these results suggest that DAPK1 is a novel regulator of tau protein abundance, and that DAPK1 upregulation might contribute to tau-related pathologies in AD. Therefore, we offer that DAPK1 might be a novel therapeutic target for treating human AD and other tau-related pathologies

Inhibition of Multidrug Resistance by SV40 Pseudovirion Delivery of an Antigene Peptide Nucleic Acid (PNA) in Cultured Cells

Peptide nucleic acid (PNA) is known to bind with extraordinarily high affinity and sequence-specificity to complementary nucleic acid sequences and can be used to suppress gene expression. However, effective delivery into cells is a major obstacle to the development of PNA for gene therapy applications. Here, we present a novel method for the in vitro delivery of antigene PNA to cells. By using a nucleocapsid protein derived from Simian virus 40, we have been able to package PNA into pseudovirions, facilitating the delivery of the packaged PNA into cells. We demonstrate that this system can be used effectively to suppress gene expression associated with multidrug resistance in cancer cells, as shown by RT-PCR, flow cytometry, Western blotting, and cell viability under chemotherapy. The combination of PNA with the SV40-based delivery system is a method for suppressing a gene of interest that could be broadly applied to numerous targets

Direct Evidence for Dominant Bond-directional Interactions in a Honeycomb Lattice Iridate Na2IrO3

Heisenberg interactions are ubiquitous in magnetic materials and have been prevailing in modeling and designing quantum magnets. Bond-directional interactions offer a novel alternative to Heisenberg exchange and provide the building blocks of the Kitaev model, which has a quantum spin liquid (QSL) as its exact ground state. Honeycomb iridates, A2IrO3 (A=Na,Li), offer potential realizations of the Kitaev model, and their reported magnetic behaviors may be interpreted within the Kitaev framework. However, the extent of their relevance to the Kitaev model remains unclear, as evidence for bond-directional interactions remains indirect or conjectural. Here, we present direct evidence for dominant bond-directional interactions in antiferromagnetic Na2IrO3 and show that they lead to strong magnetic frustration. Diffuse magnetic x-ray scattering reveals broken spin-rotational symmetry even above Neel temperature, with the three spin components exhibiting nano-scale correlations along distinct crystallographic directions. This spin-space and real-space entanglement directly manifests the bond-directional interactions, provides the missing link to Kitaev physics in honeycomb iridates, and establishes a new design strategy toward frustrated magnetism.Comment: Nature Physics, accepted (2015

Gastrointestinal stromal tumor (GIST) recurrence following surgery: review of the clinical utility of imatinib treatment

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gastrointestinal tract. Surgery with complete removal of the tumor is the primary treatment for resectable GIST and the only chance of cure. However, recurrence after surgery is common. The 2 main prognostic factors are the mitotic activity and the size of the tumor. Tumor rupture is also a risk factor for postoperative recurrence, and extra care should be taken while manipulating this soft and friable tumor. Imatinib mesylate (IM, Gleevec®, Novartis, Basel, Switzerland) is a tyrosine kinase inhibitor and was first studied in the palliative setting for metastatic GIST patients in the year 2000. It is now the cornerstone of metastatic GIST treatment. IM also plays an important role as an adjuvant treatment for resectable GIST and has been shown to increase the recurrence-free survival in phase III studies. However, some points remain to be clarified. Notably, the ideal duration of adjuvant IM after surgery is still unclear. It is also difficult to determine the exact place of surgery in metastatic or recurrent GIST patients in the IM era. A multidisciplinary approach is, therefore, mandatory to offer GIST patients the best treatment available