Crystal Nucleation in Supercooled Atomic Liquids.

The liquid-to-solid phase transition is a complex process that is difficult to investigate experimentally with sufficient spatial and temporal resolution. A key aspect of the transition is the formation of a critical seed of the crystalline phase in a supercooled liquid, that is, a liquid in a metastable state below the melting temperature. This stochastic process is commonly described within the framework of classical nucleation theory, but accurate tests of the theory in atomic and molecular liquids are challenging. Here, we employ femtosecond x-ray diffraction from microscopic liquid jets to study crystal nucleation in supercooled liquids of the rare gases argon and krypton. Our results provide stringent limits to the validity of classical nucleation theory in atomic liquids, and offer the long-sought possibility of testing nonclassical extensions of the theory.

Observation of a single protein by ultrafast X-ray diffraction.

The idea of using ultrashort X-ray pulses to obtain images of single proteins frozen in time has fascinated and inspired many. It was one of the arguments for building X-ray free-electron lasers. According to theory, the extremely intense pulses provide sufficient signal to dispense with using crystals as an amplifier, and the ultrashort pulse duration permits capturing the diffraction data before the sample inevitably explodes. This was first demonstrated on biological samples a decade ago on the giant mimivirus. Since then, a large collaboration has been pushing the limit of the smallest sample that can be imaged. The ability to capture snapshots on the timescale of atomic vibrations, while keeping the sample at room temperature, may allow probing the entire conformational phase space of macromolecules. Here we show the first observation of an X-ray diffraction pattern from a single protein, that of Escherichia coli GroEL which at 14 nm in diameter is the smallest biological sample ever imaged by X-rays, and demonstrate that the concept of diffraction before destruction extends to single proteins. From the pattern, it is possible to determine the approximate orientation of the protein. Our experiment demonstrates the feasibility of ultrafast imaging of single proteins, opening the way to single-molecule time-resolved studies on the femtosecond timescale.

N-Electron Valence Perturbation Theory with Reference Wave Functions from Quantum Computing: Application to the Relative Stability of Hydroxide Anion and Hydroxyl Radical.

Quantum simulations of the hydroxide anion and hydroxyl radical are reported, employing variational quantum algorithms for near-term quantum devices. The energy of each species is calculated along the dissociation curve, to obtain information about the stability of the molecular species being investigated. It is shown that simulations restricted to valence spaces incorrectly predict the hydroxyl radical to be more stable than the hydroxide anion. Inclusion of dynamical electron correlation from nonvalence orbitals is demonstrated, through the integration of the variational quantum eigensolver and quantum subspace expansion methods in the workflow of N-electron valence perturbation theory, and shown to correctly predict the hydroxide anion to be more stable than the hydroxyl radical, provided that basis sets with diffuse orbitals are also employed. Finally, we calculate the electron affinity of the hydroxyl radical using an aug-cc-pVQZ basis on IBM's quantum devices.

RESPONSE TO TREATMENT OF CHOROIDAL NEOVASCULARIZATION IN HIGHLY MYOPIC EYES WITH DOME-SHAPED MACULA: Two Years of Follow-Up.

PURPOSE: To compare the 2-year outcome to antivascular endothelial growth factor therapy for myopic choroidal neovascularization (CNV) in the eyes with or without dome-shaped macula (DSM). METHODS: Data from treatment-naive myopic CNV with a 2-year follow-up were retrospectively collected and divided into two groups according to the presence of DSM. The best-corrected visual acuity was acquired at baseline, 3, 12, and 24 months. The association between visual outcomes and CNV type and area, presence of scleral-derived feeder vessel, macular atrophy, and lacquer cracks at baseline was also evaluated. RESULTS: Fifty-four eyes of 54 patients were included; 18 eyes (33.4%) had DSM. Choroidal neovascularization was foveal in 10 DSM eyes (55.6%) and in 30 non-DSM eyes (83.9%), P = 0.033. At baseline, the mean best-corrected visual acuity was significantly higher in the DSM group (68.33 ± 12.04 Early Treatment Diabetic Retinopathy Study letters, 20/40 Snellen) compared with the non-DSM group (57.75 ± 13.46 Early Treatment Diabetic Retinopathy Study letters, 20/72 Snellen; P = 0.007). This difference disappeared after 3 months and did not reoccur afterward. All other parameters were not significantly associated with visual outcomes. CONCLUSION: Overall, DSM does not represent a negative prognostic factor in response to antivascular endothelial growth factor therapy in myopic CNVs after 2 years. However, in DSM eyes, CNVs tend to be extrafoveal, thus ensuring a good visual prognosis from the earliest stage of the disease.

Crystallization kinetics of atomic crystals revealed by a single-shot and single-particle X-ray diffraction experiment.

Crystallization is a fundamental natural phenomenon and the ubiquitous physical process in materials science for the design of new materials. So far, experimental observations of the structural dynamics in crystallization have been mostly restricted to slow dynamics. We present here an exclusive way to explore the dynamics of crystallization in highly controlled conditions (i.e., in the absence of impurities acting as seeds of the crystallites) as it occurs in vacuum. We have measured the early formation stage of solid Xe nanoparticles nucleated in an expanding supercooled Xe jet by means of an X-ray diffraction experiment with 10-fs X-ray free-electron laser (XFEL) pulses. We found that the structure of Xe nanoparticles is not pure face-centered cubic (fcc), the expected stable phase, but a mixture of fcc and randomly stacked hexagonal close-packed (rhcp) structures. Furthermore, we identified the instantaneous coexistence of the comparably sized fcc and rhcp domains in single Xe nanoparticles. The observations are explained by the scenario of structural aging, in which the nanoparticles initially crystallize in the highly stacking-disordered rhcp phase and the structure later forms the stable fcc phase. The results are reminiscent of analogous observations in hard-sphere systems, indicating the universal role of the stacking-disordered phase in nucleation.

Long-term natural history of highly myopic eyes with a dome-shaped macula with or without untreated serous retinal detachment: a 4-year follow-up study.

PURPOSE: To evaluate the long-term functional and morphological changes occurring in myopic eyes with a dome-shaped macula (DSM), with or without untreated serous retinal detachment (SRD). METHODS: This prospective, single-centre study enrolled consecutive cases of highly myopic patients with DSM with or without a SRD. Patients underwent complete ophthalmological examinations, optical coherence tomography, axial length measurements and autofluorescence. Follow-up visits were performed with a maximum interval of 6 months for 4 years. Eyes with choroidal neovascularisation were excluded. RESULTS: Twenty-six eyes from 18 patients (mean age 61.2) were included. At baseline, 13 eyes had SRD and 13 did not. The DSMs were either horizontal (69%) or round (31%). There were no significant differences in best-corrected visual acuity (BCVA) between eyes with and without SRD during the 48-month follow-up period. Multivariate analysis showed that baseline BCVA was the only parameter among those analysed (age and SRD height) to have a significant effect on the final BCVA (p<0.0001). SRD fluctuated overtime and SRD height was significantly influenced by choroidal thickness (p=0.002). The scleral bulge thickness had no effect on SRD thickness. CONCLUSIONS: BCVA remained clinically stable over 4 years without treatment despite the fluctuations and persistence of the SRDs.

Characterizing crystalline defects in single nanoparticles from angular correlations of single-shot diffracted X-rays.

Characterizing and controlling the uniformity of nanoparticles is crucial for their application in science and technology because crystalline defects in the nanoparticles strongly affect their unique properties. Recently, ultra-short and ultra-bright X-ray pulses provided by X-ray free-electron lasers (XFELs) opened up the possibility of structure determination of nanometre-scale matter with Å spatial resolution. However, it is often difficult to reconstruct the 3D structural information from single-shot X-ray diffraction patterns owing to the random orientation of the particles. This report proposes an analysis approach for characterizing defects in nanoparticles using wide-angle X-ray scattering (WAXS) data from free-flying single nanoparticles. The analysis method is based on the concept of correlated X-ray scattering, in which correlations of scattered X-ray are used to recover detailed structural information. WAXS experiments of xenon nanoparticles, or clusters, were conducted at an XFEL facility in Japan by using the SPring-8 Ångstrom compact free-electron laser (SACLA). Bragg spots in the recorded single-shot X-ray diffraction patterns showed clear angular correlations, which offered significant structural information on the nanoparticles. The experimental angular correlations were reproduced by numerical simulation in which kinematical theory of diffraction was combined with geometric calculations. We also explain the diffuse scattering intensity as being due to the stacking faults in the xenon clusters.

Crystal growth rates in supercooled atomic liquid mixtures.

Crystallization is a fundamental process in materials science, providing the primary route for the realization of a wide range of new materials. Crystallization rates are also considered to be useful probes of glass-forming ability1-3. At the microscopic level, crystallization is described by the classical crystal nucleation and growth theories4,5, yet in general solid formation is a far more complex process. In particular, the observation of apparently different crystal growth regimes in many binary liquid mixtures greatly challenges our understanding of crystallization1,6-12. Here, we study by experiments, theory and computer simulations the crystallization of supercooled mixtures of argon and krypton, showing that crystal growth rates in these systems can be reconciled with existing crystal growth models only by explicitly accounting for the non-ideality of the mixtures. Our results highlight the importance of thermodynamic aspects in describing the crystal growth kinetics, providing a substantial step towards a more sophisticated theory of crystal growth.

Ultrafast Structural Dynamics of Nanoparticles in Intense Laser Fields.

Femtosecond laser pulses have opened new frontiers for the study of ultrafast phase transitions and nonequilibrium states of matter. In this Letter, we report on structural dynamics in atomic clusters pumped with intense near-infrared (NIR) pulses into a nanoplasma state. Employing wide-angle scattering with intense femtosecond x-ray pulses from a free-electron laser source, we find that highly excited xenon nanoparticles retain their crystalline bulk structure and density in the inner core long after the driving NIR pulse. The observed emergence of structural disorder in the nanoplasma is consistent with a propagation from the surface to the inner core of the clusters.

Coherent Diffraction Imaging in Transmission Electron Microscopy for Atomic Resolution Quantitative Studies of the Matter.

The paper focuses on the development of electron coherent diffraction imaging in transmission electron microscopy, made in the, approximately, last ten years in our collaborative research group, to study the properties of materials at atomic resolution, overcoming the limitations due to the aberrations of the electron lenses and obtaining atomic resolution images, in which the distribution of the maxima is directly related to the specimen atomic potentials projected onto the microscope image detector. Here, it is shown how augmented coherent diffraction imaging makes it possible to achieve quantitative atomic resolution maps of the specimen atomic species, even in the presence of low atomic number atoms within a crystal matrix containing heavy atoms. This aim is achieved by: (i) tailoring the experimental set-up, (ii) improving the experimental data by properly treating parasitic diffused intensities to maximize the measure of the significant information, (iii) developing efficient methods to merge the information acquired in both direct and reciprocal spaces, (iv) treating the dynamical diffused intensities to accurately measure the specimen projected potentials, (v) improving the phase retrieval algorithms to better explore the space of solutions. Finally, some of the future perspectives of coherent diffraction imaging in a transmission electron microscope are given.

Probing Quantum Turbulence in

Theory of superfluid ^{4}He shows that, due to strong correlations and backflow effects, the density profile of a vortex line has the character of a density modulation and it is not a simple rarefaction region as found in clouds of cold bosonic atoms. We find that the basic features of this density modulation are represented by a wave packet of cylindrical symmetry in which rotons with a positive group velocity have a dominant role: The vortex density modulation can be viewed as a cloud of virtual excitations, mainly rotons, sustained by the phase of the vortex wave function. This suggests that in a vortex reconnection some of these rotons become real so that a vortex tangle is predicted to be a source of nonthermal rotons. The presence of such vorticity induced rotons can be verified by measurements at low temperature of quantum evaporation of ^{4}He atoms. We estimate the rate of evaporation and this turns out to be detectable by current instrumentation. Additional information on the microscopic processes in the decay of quantum turbulence will be obtained if quantum evaporation by high energy phonons should be detected.

Intestinal obstruction caused by endometriosis: Endoscopic stenting and expedited laparoscopic resection avoiding stoma. A case report and review of the literature.

INTRODUCTION: Endometriosis is the growth of endometrium outside the uterine cavity. In 5-15% of cases the disease can affect the colon and small bowel, causing complete obstruction and requiring resection in about 1% of cases. CASE SUMMARY: We describe a case of sigmoid obstruction due to endometriosis in a 38 years old woman with personal history of endometriosis. She was admitted for abdominal pain and constipation. The patient was treated with endoscopic stenting and subsequent laparoscopic sigmoidectomy. DISCUSSION: Bowel obstruction caused by endometriosis is a rare event. Its diagnosis can thus be a clinical and radiological challenge but it may be suspected in all young woman with colonic obstruction. At present, the management of endometriosis is an integrate approach of both medical and surgical therapy. In case of irreversible colonic obstruction surgery is mandatory. The treatment of choice is usually an emergency procedure (either Hartmann procedure or resection and anastomosis with stoma placement). This approach entails all the risks related to emergency procedures and can have important psychological and biological drawbacks. CONCLUSION: Endoscopic prosthesis placement as bridge to surgery is a feasible therapeutic strategy in colonic obstruction due to endometriosis. It brings about all the advantages of an expedited one step laparoscopic surgical procedure. Laparoscopic elective resection has a lower rate of stoma placement and has a postoperative pregnancy rate grater than open surgery.

Quantum Critical Behavior of One-Dimensional Soft Bosons in the Continuum.

We consider a zero-temperature one-dimensional system of bosons interacting via the soft-shoulder potential in the continuum, typical of dressed Rydberg gases. We employ quantum Monte Carlo simulations, which allow for the exact calculation of imaginary-time correlations, and a stochastic analytic continuation method, to extract the dynamical structure factor. At finite densities, in the weakly interacting homogeneous regime, a rotonic spectrum marks the tendency to clustering. With strong interactions, we indeed observe cluster liquid phases emerging, characterized by the spectrum of a composite harmonic chain. Luttinger theory has to be adapted by changing the reference lattice density field. In both the liquid and cluster liquid phases, we find convincing evidence of a secondary mode, which becomes gapless only at the transition. In that region, we also measure the central charge and observe its increase towards c=3/2, as recently evaluated in a related extended Bose-Hubbard model, and we note a fast reduction of the Luttinger parameter. For two-particle clusters, we then interpret such observations in terms of the compresence of a Luttinger liquid and a critical transverse Ising model, related to the instability of the reference lattice density field towards coalescence of sites, typical of potentials which are flat at short distances. Even in the absence of a true lattice, we are able to evaluate the spatial correlation function of a suitable pseudospin operator, which manifests ferromagnetic order in the cluster liquid phase, exponential decay in the liquid phase, and algebraic order at criticality.

Facing the phase problem in Coherent Diffractive Imaging via Memetic Algorithms.

Coherent Diffractive Imaging is a lensless technique that allows imaging of matter at a spatial resolution not limited by lens aberrations. This technique exploits the measured diffraction pattern of a coherent beam scattered by periodic and non-periodic objects to retrieve spatial information. The diffracted intensity, for weak-scattering objects, is proportional to the modulus of the Fourier Transform of the object scattering function. Any phase information, needed to retrieve its scattering function, has to be retrieved by means of suitable algorithms. Here we present a new approach, based on a memetic algorithm, i.e. a hybrid genetic algorithm, to face the phase problem, which exploits the synergy of deterministic and stochastic optimization methods. The new approach has been tested on simulated data and applied to the phasing of transmission electron microscopy coherent electron diffraction data of a SrTiO3 sample. We have been able to quantitatively retrieve the projected atomic potential, and also image the oxygen columns, which are not directly visible in the relevant high-resolution transmission electron microscopy images. Our approach proves to be a new powerful tool for the study of matter at atomic resolution and opens new perspectives in those applications in which effective phase retrieval is necessary.

Novel behavior of monolayer quantum gases on graphene, graphane and fluorographene.

This article discusses the behavior of submonolayer quantum films (He and H2) on graphene and newly discovered surfaces that are derived from graphene. Among these substrates are graphane (abbreviated GH), which has an H atom bonded to each C atom, and fluorographene (GF). The subject is introduced by describing the related problem of monolayer films on graphite. For that case, extensive experimental and theoretical investigations have revealed that the phase diagrams of the Bose gases (4)He and para-H2 are qualitatively similar, differing primarily in a higher characteristic temperature scale for H2 than for He. The phase behavior of these films on one side of pristine graphene, or both sides of free-standing graphene, is expected to be similar to that on graphite. We point out the possibility of novel phenomena in adsorption on graphene related to the large flexibility of the graphene sheet, to the non-negligible interaction between atoms adsorbed on opposite sides of the sheet and to the perturbation effect of the adsorbed layer on the Dirac electrons. In contrast, the behavior predicted on GF and GH surfaces is very different from that on graphite, a result of the different corrugation, i.e., the lateral variation of the potential experienced by these gases. This arises because on GF, for example, half of the F atoms are located above the C plane while the other half are below this plane. Hence, the He and H2 gases experience very different potentials from those on graphite or graphene. As a result of this novel geometry and potential, distinct properties are observed. For example, the (4)He film's ground state on graphite is a two-dimensional (2D) crystal commensurate with the substrate, the famous [Formula: see text] phase; on GF and GH, instead, it is predicted to be an anisotropic superfluid. On GF the anisotropy is so extreme that the roton excitations are very anisotropic, as if the bosons are moving in a multiconnected space along the bonds of a honeycomb lattice. Such a novel phase has not been predicted or observed previously on any substrate. Also, in the case of (3)He the film's ground state is a fluid, thus offering the possibility of studying an anisotropic Fermi fluid with a tunable density. The exotic properties expected for these films are discussed along with proposed experimental tests.

The use of biological mesh to repair one large, contaminated abdominal wall defect due to neoplastic invasion. Report of a case.

We hereby report a case of use of biological mesh to repair one large, contaminated abdominal wall defect due to a sigmoid tumour presented as an abscess infiltrating the abdominal wall. Our patient was a 48-year-old woman. Her medical history was negative for any previous disease or surgical procedure. Because of the abscence of neoplastic secondarism an en-bloc resection of the interested sigmoid colon and of the infiltrated abdominal wall was performed, thus resulting a large wall defect in the left inguinal region. In order to close the wall defect a biological porcine collagen mesh was used. In our case we used a Permacol mesh made of porcine acellular dermal collagen. Reconstruction of complicated abdominal wall defects is a challenging surgical problem and primary repair is often difficult to achieve without excessive tension in the abdominal wall. The use of a syntethic mesh in this patient could have been inappropriate due to the possibility of creating adhesions with intra-abdominal viscera and fistula formation. We chose to use a biological mesh because of its safer properties in case of infected, inflamed or infiltrated surgical fields, as demonstrated in the literature.

Usefulness of Preoperative Diagnosis with Magnetic Resonance Imaging for Conservative Surgery in Paget's Disease of the Breast.

BACKGROUND: Paget's disease (PD) of the breast is a relatively rare condition (incidence 1-3%) among primary breast cancers [6]. It presents with suggestive symptoms like erythema, nipple bleeding and ulceration. PATIENT AND METHODS: A 76-year-old woman was followed up for cancer of the left breast that had been operated 10 years before. During her annual check, a lesion suggestive of PD was detected. Mammography and ultrasound were performed, without evidence of a new breast lesion. In consideration of a possible underestimation of the real extent of the disease, we performed magnetic resonance imaging (MRI). RESULTS: MRI showed an irregularly shaped tissue infiltrating the external side of the right breast. The pathologically bright signal involved the nipple and deformed the areolar skin. The characteristics of the increased signal were typical of a hypervascular invasive pattern and for tumoral neoangiogenesis. We performed a mastectomy with sentinel lymph node (SLN) biopsy, with evidence of a DIN 3 carcinoma associated with PD of the nipple at the final pathology report. CONCLUSION: The MRI was instrumental for the assessment of the existence and extent of malignant disease in a patient with PD but without a palpable lesion detectable with negative ultrasound and mammography.

Multicenter clinical assessment of the Raumedic Neurovent-P intracranial pressure sensor: a report by the BrainIT group.

OBJECTIVE: The aim of this study was to evaluate the robustness and zero-drift of an intracranial pressure sensor, Neurovent-P (Raumedic AG, Münchberg, Germany), when used in the clinical environment. METHODS: A prospective multicenter trial, conforming to the International Organization for Standardization 14155 Standard, was conducted in 6 European BrainIT centers between July 2005 and December 2006. Ninety-nine catheters were used. The study was observational, followed by a centralized sensor bench test after catheter removal. RESULTS: The mean recorded value before probe insertion was 0.17 +/- 1.1 mm Hg. Readings outside the range +/-1 mm Hg were recorded in only 3 centers on a total of 15 catheters. Complications were minimal and mainly related to the insertion bolt. The mean recorded pressure value at removal was 0.8 +/- 2.2 mm Hg. No relationship was identified between postremoval reading and length of monitoring. The postremoval bench test indicated the probability of a system failure, defined as a drift of more than 3 mm Hg, at a range between 12 and 17%. CONCLUSION: The Neurovent-P catheter performed well in clinical use in terms of robustness. The majority of technical complications were associated with the bolt fixation technology. Adverse events were rare and clinically nonsignificant. Despite the earlier reported excellent bench test zero-drift rates, under the more demanding clinical conditions, zero-drift rate remains a concern with catheter tip strain gauge technology. This performance is similar, and not superior, to other intracranial pressure devices.