722 research outputs found

    Towards Visual Foundational Models of Physical Scenes

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    We describe a first step towards learning general-purpose visual representations of physical scenes using only image prediction as a training criterion. To do so, we first define "physical scene" and show that, even though different agents may maintain different representations of the same scene, the underlying physical scene that can be inferred is unique. Then, we show that NeRFs cannot represent the physical scene, as they lack extrapolation mechanisms. Those, however, could be provided by Diffusion Models, at least in theory. To test this hypothesis empirically, NeRFs can be combined with Diffusion Models, a process we refer to as NeRF Diffusion, used as unsupervised representations of the physical scene. Our analysis is limited to visual data, without external grounding mechanisms that can be provided by independent sensory modalities.Comment: TLDR: Physical scenes are equivalence classes of sufficient statistics, and can be inferred uniquely by any agent measuring the same finite data; We formalize and implement an approach to representation learning that overturns "naive realism" in favor of an analytical approach of Russell and Koenderink. NeRFs cannot capture the physical scenes, but combined with Diffusion Models they ca

    Monopoles and Holography

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    We present a holographic theory in AdS_4 whose zero temperature ground state develops a crystal structure, spontaneously breaking translational symmetry. The crystal is induced by a background magnetic field, but requires no chemical potential. This lattice arises from the existence of 't Hooft-Polyakov monopole solitons in the bulk which condense to form a classical object known as a monopole wall. In the infra-red, the magnetic field is screened and there is an emergent SU(2) global symmetry.Comment: 33 pages, 16 figures; v2: ref adde

    Spin dynamics of molecular nanomagnets fully unraveled by four-dimensional inelastic neutron scattering

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    Molecular nanomagnets are among the first examples of spin systems of finite size and have been test-beds for addressing a range of elusive but important phenomena in quantum dynamics. In fact, for short-enough timescales the spin wavefunctions evolve coherently according to the an appropriate cluster spin-Hamiltonian, whose structure can be tailored at the synthetic level to meet specific requirements. Unfortunately, to this point it has been impossible to determine the spin dynamics directly. If the molecule is sufficiently simple, the spin motion can be indirectly assessed by an approximate model Hamiltonian fitted to experimental measurements of various types. Here we show that recently-developed instrumentation yields the four-dimensional inelastic-neutron scattering function S(Q,E) in vast portions of reciprocal space and enables the spin dynamics to be determined with no need of any model Hamiltonian. We exploit the Cr8 antiferromagnetic ring as a benchmark to demonstrate the potential of this new approach. For the first time we extract a model-free picture of the quantum dynamics of a molecular nanomagnet. This allows us, for example, to examine how a quantum fluctuation propagates along the ring and to directly test the degree of validity of the N\'{e}el-vector-tunneling description of the spin dynamics

    Brain metastases from solid tumors: disease outcome according to type of treatment and therapeutic resources of the treating center

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    <p>Abstract</p> <p>Background</p> <p>To evaluate the therapeutic strategies commonly employed in the clinic for the management of brain metastases (BMs) and to correlate disease outcome with type of treatment and therapeutic resources available at the treating center.</p> <p>Methods</p> <p>Four Cancer centres participated to the survey. Data were collected through a questionnaire filled in by one physician for each centre.</p> <p>Results</p> <p>Clinical data regarding 290 cancer patients with BMs from solid tumors were collected. Median age was 59 and 59% of patients had ≤ 3 brain metastases. A local approach (surgery and stereotactic radiosurgery) was adopted in 31% of patients. The local approach demonstrated to be superior in terms of survival compared to the regional/systemic approach (whole brain radiotherapy and chemotherapy, p = <.0001 for survival at 2 years). In the multivariate analysis local treatment was an independent prognostic factor for survival. When patients were divided into 2 groups whether they were treated in centers where local approaches were available or not (group A vs group B respectively, 58% of patients with ≤ 3 BMs in both cohorts), more patients in group A received local strategies although no difference in time to brain progression at 1 year was observed between the two groups of patients.</p> <p>Conclusions</p> <p>In clinical practice, local strategies should be integrated in the management of brain metastases. Proper selection of patients who are candidate to local treatments is of crucial importance.</p

    Strong Ultraviolet Pulse From a Newborn Type Ia Supernova

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    Type Ia supernovae are destructive explosions of carbon oxygen white dwarfs. Although they are used empirically to measure cosmological distances, the nature of their progenitors remains mysterious, One of the leading progenitor models, called the single degenerate channel, hypothesizes that a white dwarf accretes matter from a companion star and the resulting increase in its central pressure and temperature ignites thermonuclear explosion. Here we report observations of strong but declining ultraviolet emission from a Type Ia supernova within four days of its explosion. This emission is consistent with theoretical expectations of collision between material ejected by the supernova and a companion star, and therefore provides evidence that some Type Ia supernovae arise from the single degenerate channel.Comment: Accepted for publication on the 21 May 2015 issue of Natur

    Cigarette smoke-induced pulmonary emphysema in scid-mice. Is the acquired immune system required?

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    BACKGROUND: Chronic obstructive pulmonary disease is associated with a chronic inflammatory response of the host to chronic exposure to inhaled toxic gases and particles. Although inflammatory cells of both the innate and adaptive immune system infiltrate the lungs in pulmonary emphysema and form lymphoid follicles around the small airways, the exact role of the acquired immune system in the pathogenesis of emphysema is not known. METHODS: In this study, wild type Balb/c mice and immunodeficient scid mice – which lack functional B- and T-cells – were exposed to mainstream cigarette smoke (CS) for 5 weeks or 6 months. RESULTS: Subacute CS-exposure for 5 weeks significantly increased innate inflammatory cells (neutrophils, macrophages and dendritic cells) in the bronchoalveolar lavage (BAL) fluid of wild type mice and scid mice, which correlated with the CS-induced upregulation of the chemokines Monocyte Chemotactic Protein-1, Macrophage Inflammatory Protein-3α and KC (= mouse Interleukin-8). Chronic CS-exposure for 6 months significantly increased the number of neutrophils, macrophages, dendritic cells, CD4(+ )and CD8(+ )T-lymphocytes in BAL fluid and lungs of wild type mice compared to air-exposed littermates, and augmented the size and number of peribronchial lymphoid follicles. In contrast, neither B-lymphocytes, nor T-lymphocytes, nor lymphoid follicles could be discerned in the lungs of air- or CS-exposed scid mice. Importantly, chronic CS-exposure induced pulmonary emphysema in both wild type animals and scid mice, as evidenced by a significant increase in the mean linear intercept and the destructive index of CS-exposed versus air-exposed animals. The CS-induced emphysema was associated with increased mRNA expression of matrix metalloproteinase-12 in the lungs and increased protein levels of Tumor Necrosis Factor-α in the BAL fluid of CS-exposed Balb/c and scid mice compared to air-exposed littermates. CONCLUSION: This study suggests that the adaptive immune system is not required per se to develop pulmonary emphysema in response to chronic CS-exposure, since emphysema can be induced in scid mice, which lack lymphoid follicles as well as functional B- and T-cells

    Congenital aplasia of the optic chiasm and esophageal atresia: a case report

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    <p>Abstract</p> <p>Introduction</p> <p>The complete absence of the chiasm (chiasmal aplasia) is a rare clinical condition. Hypoplasia of the optic nerve and congenital nystagmus are almost invariably associated characteristics. Microphthalmos or anophthalmos are common features in chiasmal aplasia, while central nervous system abnormalities are less frequent. Esophageal atresia can be isolated or syndromic. In syndromic cases, it is frequently associated with cardiac, limb, renal or vertebral malformations and anal atresia. More rarely, esophageal atresia can be part of anophthalmia-esophageal-genital syndrome, which comprises anophthalmia or microphthalmia, genital abnormalities, vertebral defects and cerebral malformations. Here, a previously unreported case of chiasmal aplasia presenting without microphthalmos and associated with esophageal atresia is described.</p> <p>Case presentation</p> <p>Aplasia of the optic chiasm was identified in a Caucasian Italian 8-month-old boy with esophageal atresia. An ultrasound examination carried out at 21 weeks' gestation revealed polyhydramnios. Intrauterine growth retardation, esophageal atresia and a small atrial-septal defect were subsequently detected at 28 weeks' gestation. Repair of the esophageal atresia was carried out shortly after birth. A jejunostomy was carried out at four months to facilitate enteral feeding. The child was subsequently noted to be visually inattentive and to be neurodevelopmentally delayed. Magnetic resonance imaging revealed chiasmal aplasia. No other midline brain defects were found. His karyotype was normal.</p> <p>Conclusion</p> <p>If achiasmia is a spectrum, our patient seems to depict the most severe form, since he appears to have an extremely severe visual impairment. This is in contrast to most of the cases described in the literature, where patients maintain good--or at least useful-- visual function. To the best of our knowledge, the association of optic nerve hypoplasia, complete chiasmal aplasia, esophageal atresia and atrial-septal defect, choanal atresia, hypertelorism and psychomotor retardation has never been described before.</p

    Establishment of LIF-Dependent Human iPS Cells Closely Related to Basic FGF-Dependent Authentic iPS Cells

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    Human induced pluripotent stem cells (iPSCs) can be divided into a leukemia inhibitory factor (LIF)-dependent naïve type and a basic fibroblast growth factor (bFGF)-dependent primed type. Although the former are more undifferentiated than the latter, they require signal transduction inhibitors and sustained expression of the transgenes used for iPSC production. We used a transcriptionally enhanced version of OCT4 to establish LIF-dependent human iPSCs without the use of inhibitors and sustained transgene expression. These cells belong to the primed type of pluripotent stem cell, similar to bFGF-dependent iPSCs. Thus, the particular cytokine required for iPSC production does not necessarily define stem cell phenotypes as previously thought. It is likely that the bFGF and LIF signaling pathways converge on unidentified OCT4 target genes. These findings suggest that our LIF-dependent human iPSCs could provide a novel model to investigate the role of cytokine signaling in cellular reprogramming

    Phase Ia clinical evaluation of the safety and immunogenicity of the Plasmodium falciparum blood-stage antigen AMA1 in ChAd63 and MVA vaccine vectors.

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    BACKGROUND: Traditionally, vaccine development against the blood-stage of Plasmodium falciparum infection has focused on recombinant protein-adjuvant formulations in order to induce high-titer growth-inhibitory antibody responses. However, to date no such vaccine encoding a blood-stage antigen(s) alone has induced significant protective efficacy against erythrocytic-stage infection in a pre-specified primary endpoint of a Phase IIa/b clinical trial designed to assess vaccine efficacy. Cell-mediated responses, acting in conjunction with functional antibodies, may be necessary for immunity against blood-stage P. falciparum. The development of a vaccine that could induce both cell-mediated and humoral immune responses would enable important proof-of-concept efficacy studies to be undertaken to address this question. METHODOLOGY: We conducted a Phase Ia, non-randomized clinical trial in 16 healthy, malaria-naïve adults of the chimpanzee adenovirus 63 (ChAd63) and modified vaccinia virus Ankara (MVA) replication-deficient viral vectored vaccines encoding two alleles (3D7 and FVO) of the P. falciparum blood-stage malaria antigen; apical membrane antigen 1 (AMA1). ChAd63-MVA AMA1 administered in a heterologous prime-boost regime was shown to be safe and immunogenic, inducing high-level T cell responses to both alleles 3D7 (median 2036 SFU/million PBMC) and FVO (median 1539 SFU/million PBMC), with a mixed CD4(+)/CD8(+) phenotype, as well as substantial AMA1-specific serum IgG responses (medians of 49 µg/mL and 41 µg/mL for 3D7 and FVO AMA1 respectively) that demonstrated growth inhibitory activity in vitro. CONCLUSIONS: ChAd63-MVA is a safe and highly immunogenic delivery platform for both alleles of the AMA1 antigen in humans which warrants further efficacy testing. ChAd63-MVA is a promising heterologous prime-boost vaccine strategy that could be applied to numerous other diseases where strong cellular and humoral immune responses are required for protection. TRIAL REGISTRATION: ClinicalTrials.gov NCT01095055
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