Negative linear compressibility in Se at ultra-high pressure above 120 GPa.

A series of in situ synchrotron X-ray diffraction (XRD) measurements were carried out, combined with first-principles calculations, to study structural phase transitions of selenium at high pressures and room temperature. Several phase transitions were observed, among which an isostructural phase transition was found at around 120 GPa for the first time. Evolved from the rhombohedral (space group R 3 m) structure (Se-V), the new phase (Se-V') exhibited an interesting increase of lattice parameter a at pressures from 120 to 148 GPa, known as negative linear compressibility (NLC). The discovery of NLC behavior observed in this work is mainly attributed to the accuracy and fine steps controlled by the membrane system for in situ XRD data collected with an exposure time of 0.5 s. After 140 GPa, a body-centered cubic (b.c.c.) structure Se-VI (space group Im 3 m) was formed, which remains stable up to 210 GPa, the highest pressure achieved in this study. The bulk moduli of phases Se-V, Se-V' and Se-VI were estimated to be 83 ± 2, 321 ± 2 and 266 ± 7 GPa, respectively, according to the P-V curve fit by the third-order Birch-Murnaghan equation of state. The Se-V' phase shows a bulk modulus almost 4 times larger than that of the Se-V phase, which is mainly due to the effect of its NLC. NLC in a higher pressure range is always more significant in terms of fundamental mechanism and new materials discovery, yet it has barely been reported at pressures above 100 GPa. This will hopefully inspire future studies on potential NLC behaviors in other materials at ultra-high pressure.

Topological Ordering of Memory Glass on Extended Length Scales.

Identifying ordering in non-crystalline solids has been a focus of natural science since the publication of Zachariasen's random network theory in 1932, but it still remains as a great challenge of the century. Literature shows that the hierarchical structures, from the short-range order of first-shell polyhedra to the long-range order of translational periodicity, may survive after amorphization. Here, in a piece of AlPO4, or berlinite, we combine X-ray diffraction and stochastic free-energy surface simulations to study its phase transition and structural ordering under pressure. From reversible single crystals to amorphous transitions, we now present an unambiguous view of the topological ordering in the amorphous phase, consisting of a swarm of Carpenter low-symmetry phases with the same topological linkage, trapped in a metastable intermediate stage. We propose that the remaining topological ordering is the origin of the switchable "memory glass" effect. Such topological ordering may hide in many amorphous materials through disordered short atomic displacements.

Pressure tuned incommensurability and guest structure transition in compressed scandium from machine learning atomic simulation.

Scandium (Sc) is the lightest non-main-group element and transforms to a host-guest (H-G) incommensurate structure under gigapascal (GPa) pressures. While the host structure is stable over a wide pressure range, the guest structure may exist in multiple forms, featuring different incommensurate ratios, and mixing up to generate long-range "disordered" guest structures. Here, we employed the recently developed global neural network (g-NN) potential and the stochastic surface walking (SSW) global optimization algorithm to explore the global potential energy surface of Sc under various pressures. We probe the global minima structure in a system made of hundreds of atoms and revealed that the solid-phase transition between Sc-I and H-G Sc-II phases is fully reconstructive in nature. Above 62.5 GPa, the pressure will further destabilize the face-centered tetragonal (fct, Sc-IIa) guest structure to a body-centered tetragonal phase (bct, Sc-IIb), while sustaining the host structure. The structural transition mechanism of this work will shed light on the nature of the complex H-G structural modifications in compressed metals.

Unraveling the structural transition mechanism of room-temperature compressed graphite carbon.

The discovery of graphite transition to transparent and superhard carbons under room-temperature compression (Takehiko, et al., Science, 1991, 252, 1542 and Mao, et al., Science, 2003, 302, 425) launched decades of intensive research into carbon's structural polymorphism and relative phase transition mechanisms. Although many possible carbon allotropes have been proposed, experimental observations and their transition mechanisms are far from conclusive. Three longstanding issues are: (i) the speculative structures inferred by amorphous-like XRD peaks, (ii) sp2 and sp3 bonding mixing, and (iii) the controversies of transition reversibility. Here, by utilizing the stochastic surface walking method for unbiased pathway sampling, we resolve the possible atomic structure and the lowest energy pathways between multiple carbon allotropes under high pressure. We found that a new transition pathway, through which graphite transits to a highly disordered phase by shearing the boat architecture line atoms out of the graphite (001) plane upward or downward featuring without the nuclei core, is the most favorable. This transition pathway facilitates the generation of a variety of equally favorable carbon structures that are controlled by the local strain and crystal orientation, resembling structural disordering. Our results may help to understand the nature of graphite under room temperature compression.

Structure-Controlled Oxygen Concentration in Fe2O3 and FeO2.

Solid-solid reaction, particularly in the Fe-O binary system, has been extensively studied in the past decades because of its various applications in chemistry and materials and earth sciences. The recently synthesized pyrite-FeO2 at high pressure suggested a novel oxygen-rich stoichiometry that extends the achievable O-Fe ratio in iron oxides by 33%. Although FeO2 was synthesized from Fe2O3 and O2, the underlying solid reaction mechanism remains unclear. Herein, combining in situ X-ray diffraction experiments and first-principles calculations, we identified that two competing phase transitions starting from Fe2O3: (1) without O2, perovskite-Fe2O3 transits to the post-perovskite structure above 50 GPa; (2) if free oxygen is present, O diffuses into the perovskite-type lattice of Fe2O3 leading to the pyrite-type FeO2 phase. We found the O-O bonds in FeO2 are formed by the insertion of oxygen into the Pv lattice via the external stress and such O-O bonding is only kinetically stable under high pressure. This may provide a general mechanism of adding extra oxygen to previous known O saturated oxides to produce unconventional stoichiometries. Our results also shed light on how O is enriched in mantle minerals under pressure.

Photoselective Vaporesection of the Prostate via an End-firing Lithium Triborate Crystal Laser.

The occurrence of lower urinary tract symptoms (LUTS) caused by benign prostatic hyperplasia (BPH) is a common problem with a high incidence in the aging male population. Although it is not a life-threatening disease, BPH causes problems that seriously impact the quality of life. Here, we introduce a new technique called photoselective vaporesection of the prostate (PVRP) in treating BPH, which can be seen as a variation of photoselective vaporization of the prostate (PVP). This procedure presents several advantages compared to the PVP technique including less laser energy loss, less intraoperative complications as well as more tissue resection rate.

Hydrogen-Bond Symmetrization Breakdown and Dehydrogenation Mechanism of FeO2H at High Pressure.

The cycling of hydrogen plays an important role in the geochemical evolution of our planet. Under high-pressure conditions, asymmetric hydroxyl bonds tend to form a symmetric O-H-O configuration in which H is positioned at the center of two O atoms. The symmetrization of O-H bonds improves their thermal stability and as such, water-bearing minerals can be present deeper in the Earth's lower mantle. However, how exactly H is recycled from the deep mantle remains unclear. Here, we employ first-principles free-energy landscape sampling methods together with high pressure-high temperature experiments to reveal the dehydrogenation mechanism of a water-bearing mineral, FeO2H, at deep mantle conditions. Experimentally, we show that ∼50% H is released from symmetrically hydrogen-bonded ε-FeO2H upon transforming to a pyrite-type phase (Py-phase). By resolving the lowest-energy transition pathway from ε-FeO2H to the Py-phase, we demonstrate that half of the O-H bonds in the mineral rupture during the structural transition, leading toward the breakdown of symmetrized hydrogen bonds and eventual dehydrogenation. Our study sheds new light on the stability of symmetric hydrogen bonds during structural transitions and provides a dehydrogenation mechanism for hydrous minerals existing in the deep mantle.

Fractal MTW Zeolite Crystals: Hidden Dimensions in Nanoporous Materials.

Screw dislocation structures in crystals are an origin of symmetry breaking in a wide range of dense-phase crystals. Preparation of such analogous structures in framework-phase crystals is of great importance in zeolites but is still a challenge. On the basis of crystal-structure solving and model building, it was found that the two specific intergrowths in MTW zeolite produce this complex fractal and spiral structure. With the structurally determined parameters (spiral pitch h, screw angle θ, and spatial angle ψ) of Burgers circuit, the screw dislocation structure can be constructed by two different dimensional intergrowth sections. Thus the reported complexity of various dimensions in diverse crystals can be unified.

Photoselective Vaporesection of the Prostate with an End-firing Lithium Triborate Crystal Laser.

BACKGROUND: Photoselective vaporization of the prostate is a technique that is widely used for the treatment of benign prostatic hyperplasia (BPH) and has pronounced advantages compared to the traditional transurethral resection of the prostate. Following the recent introduction of end-firing lithium triborate lasers, we have created a new technique called photoselective vaporesection of the prostate (PVRP). This study described our initial experience using the PVRP technique for the treatment of BPH. METHODS: This prospective study included a total of 35 patients with BPH who underwent PVRP from August 2013 to July 2014. The chief clinical parameters were obtained and evaluated during the perioperative period and follow-up, including the International Prostate Symptom Score (IPSS), quality of life (QoL) score, maximum urinary flow rate, and prostate volume. All variables were evaluated for statistically significant differences compared to baseline values using the analysis of variance. RESULTS: The mean subgroup IPSS and QoL scores significantly improved during follow-up; the respective decreases in IPSS storage score, IPSS voiding score, IPSS nocturia score, and QoL score were 75.3%, 83.6%, 51.4%, and 71.7%, respectively (all P < 0.001 compared with baseline). Three patients were diagnosed with prostate cancer based on postoperative pathological examinations. There were no serious perioperative complications. CONCLUSION: The PVRP technique demonstrates satisfactory short-term clinical outcomes and perioperative safety in the treatment of BPH.

Mechanism and microstructures in Ga2O3 pseudomartensitic solid phase transition.

Solid-to-solid phase transition, although widely exploited in making new materials, challenges persistently our current theory for predicting its complex kinetics and rich microstructures in transition. The Ga2O3α-ß phase transformation represents such a common but complex reaction with marked change in cation coordination and crystal density, which was known to yield either amorphous or crystalline products under different synthetic conditions. Here we, via recently developed stochastic surface walking (SSW) method, resolve for the first time the atomistic mechanism of Ga2O3α-ß phase transformation, the pathway of which turns out to be the first reaction pathway ever determined for a new type of diffusionless solid phase transition, namely, pseudomartensitic phase transition. We demonstrate that the sensitivity of product crystallinity is caused by its multi-step, multi-type reaction pathway, which bypasses seven intermediate phases and involves all types of elementary solid phase transition steps, i.e. the shearing of O layers (martensitic type), the local diffusion of Ga atoms (reconstructive type) and the significant lattice dilation (dilation type). While the migration of Ga atoms across the close-packed O layers is the rate-determining step and yields "amorphous-like" high energy intermediates, the shearing of O layers contributes to the formation of coherent biphase junctions and the presence of a crystallographic orientation relation, (001)α//(201[combining macron])ß + [120]α//[13[combining macron]2]ß. Our experiment using high-resolution transmission electron microscopy further confirms the theoretical predictions on the atomic structure of biphase junction and the formation of (201[combining macron])ß twin, and also discovers the late occurrence of lattice expansion in the nascent ß phase that grows out from the parent α phase. By distinguishing pseudomartensitic transition from other types of mechanisms, we propose general rules to predict the product crystallinity of solid phase transition. The new knowledge on the kinetics of pseudomartensitic transition complements the theory of diffusionless solid phase transition.

Reaction Network of Layer-to-Tunnel Transition of MnO2.

As a model system of 2-D oxide material, layered δ-MnO2 has important applications in Li ion battery systems. δ-MnO2 is also widely utilized as a precursor to synthesize other stable structure variants in the MnO2 family, such as α-, ß-, R-, and γ-phases, which are 3-D interlinked structures with different tunnels. By utilizing the stochastic surface walking (SSW) pathway sampling method, we here for the first time resolve the atomistic mechanism and the kinetics of the layer-to-tunnel transition of MnO2, that is, from δ-MnO2 to the α-, ß-, and R-phases. The SSW sampling determines the lowest-energy pathway from thousands of likely pathways that connects different phases. The reaction barriers of layer-to-tunnel phase transitions are found to be low, being 0.2-0.3 eV per formula unit, which suggests a complex competing reaction network toward different tunnel phases. All the transitions initiate via a common shearing and buckling movement of the MnO2 layer that leads to the breaking of the Mn-O framework and the formation of Mn(3+) at the transition state. Important hints are thus gleaned from these lowest-energy pathways: (i) the large pore size product is unfavorable for the entropic reason; (ii) cations are effective dopants to control the kinetics and selectivity in layer-to-tunnel transitions, which in general lowers the phase transition barrier and facilitates the creation of larger tunnel size; (iii) the phase transition not only changes the electronic structure but also induces the macroscopic morphology changes due to the interfacial strain.

Nature of Rutile Nuclei in Anatase-to-Rutile Phase Transition.

The solid phase transition of TiO2, in particular anatase to rutile, has been extensively studied in the past 30 years. To seek the nucleation site at the beginning of phase transition is highly challenging, which asks for new theoretical techniques with high spatial and temporal resolution. This work reports the first evidence on the atomic structure of the nucleation sites in the TiO2 anatase-to-rutile phase transition. Novel automated theoretical methods, namely stochastic surface walking based pathway sampling methods, are utilized to resolve the lowest energy pathways at the initial stage of phase transition. We show that among common anatase surfaces, only the (112) ridged surface provides the nucleation site for phase transition, which can lead to the formation of both TiO2-II and brookite thin slabs. The TiO2-II phase is kinetically preferred product; the propagation into the subsurface is still hindered by high barriers that is the origin for the slow kinetics of nuclei formation. The rutile nuclei are thus not rutile phase but nascent metastable TiO2-II phase in an anatase matrix. The phase transition kinetics is found to be sensitive to the compressive strain and the crystallographic directions. The results rationalize the size and morphology dependence of the anisotropic phase transition kinetics of anatase particles and could facilitate the rational design of material via controlled solid phase transition.

Three-phase junction for modulating electron-hole migration in anatase-rutile photocatalysts.

The heterophase solid-solid junction as an important type of structure unit has wide applications for its special mechanics and electronic properties. Here we present a first three-phase atomic model for the anatase-rutile TiO2 heterophase junction and determine its optical and electronic properties, which leads to resolution of the long-standing puzzles on the enhanced photocatalytic activity of anatase-rutile photocatalysts. By using a set of novel theoretical methods, including crystal phase transition pathway sampling, interfacial strain analysis and first principles thermodynamics evaluation of holes and electrons, we identify an unusual structurally ordered three-phase junction, a layer-by-layer "T-shaped" anatase/TiO2-II/rutile junction, for linking anatase with rutile. The intermediate TiO2-II phase, although predicted to be only a few atomic layers thick in contact with anatase, is critical to alleviate the interfacial strain and to modulate photoactivity. We demonstrate that the three-phase junction acts as a single-way valve allowing the photogenerated hole transfer from anatase to rutile but frustrating the photoelectron flow in the opposite direction, which otherwise cannot be achieved by an anatase-rutile direct junction. This new model clarifies the roles of anatase, rutile and the phase junction in achieving high photoactivity synergistically and provides the theoretical basis for the design of better photocatalysts by exploiting multi-phase junctions.

Design and Observation of Biphase TiO2 Crystal with Perfect Junction.

Bicrystalline materials have wide applications from silicon chips to photocatalysis, but the controlled synthesis of nanocrytals with ordered phase junction has been challenging, in particular via chemical synesthetic routes. Here, we propose a general strategy to design biphase crystals formed via partial solid-to-solid phase transition with perfect phase junction, e.g., being atomically sharp and built of two particular sets of epitaxially joined planes of the two component phases, and present such an example by designing, synthesizing, and characterizing the interface of two TiO2 phases, namely, TiO2-B/anatase biphase nanocrystals that are obtained conveniently via one-pot chemical synthesis. Our design strategy classifies the common solid-to-solid phase transition into three types that are distinguishable by using the newly developed stochastic surface walking (SSW) method for unbiased pathway sampling. Only Type-I crystal is predicted to possess perfect phase junction, where the phase transition involves one and only one propagation direction featuring single pathway phase transition containing only one elementary kinetic step. The method is applicable for the understanding and the design of heterophase materials via partial phase transition in general.

[Comparison of natural orifice transumbilical endoscopic surgery versus conventional laparoscopic surgery in renal cyst deroofing].

OBJECTIVE: To compare the safety and feasibility of natural orifice transumbilical endoscopic surgery (NOTES) versus conventional laparoscopic surgery in renal cyst deroofing. METHODS: From May 2010 to August 2011, 8 cases of renal cysts underwent cyst deroofing by the technique of NOTES (Triport) (group A) and 14 cases by conventional laparoscopic surgery (Group B) respectively. The data of patient age, cyst size, operative duration, estimated blood loss, intra-operative complications, drainage duration, post-operative pain score (VAPS) and post-operative hospital stay were recorded and analyzed. RESULTS: The average cyst sizes of groups A and B were 6.6 ± 2.4 and 7.0 ± 2.5 cm. There was no conversion to open surgery in neither groups and no conversion to standard laparoscopic surgery in group A. The operative duration, estimated blood volume, VAPS and post-operative hospital stay of both groups were 49 vs 35 min, 12 vs 10 ml, 0 vs 1 and 4 vs 5 days respectively. The drainage duration was 1 day for both groups. No severe complication, secondary hemorrhage or wound infection occurred in neither groups. As judged by both surgeons and patients, the post-operative cosmetic appearances of group A were better than those of group B. CONCLUSION: The cyst deroofing by NOTES is a safe and feasible option for the treatment of renal cysts. As compared with conventional laparoscopic surgery, NOTES may achieve better cosmetic effects with smaller wounds.

[Study on patients with benign prostate hyperplasia treated by the therapeutic regimen of watchful waiting during a twenty-four-month follow-up period].

OBJECTIVE: To analyze the changes of the main clinic parameters in patients with benign prostate hyperplasia (BPH) treated by watchful waiting and to find out the risk factors contributing the progress of BPH. METHODS: According to the inclusion and exclusion criteria,61 patients diagnosed as BPH were recruited in the group of watchful waiting. Data on IPSS, prostate volume, prostate specific antigen (PSA), maximum flow rate, average flow rate and residual urine volume during follow-up period of 24 months, were recorded. RESULTS: At 0, 12, 24 months, the IPSS, prostate volume (ml), PSA(ng/ml), maximum flow rate (ml/s) were 7 +/- 4, 4 +/- 3, 4 +/- 3; 33.0 +/- 9.0, 33.8 +/- 7.6, 30.9 +/- 6.8; 1.53 +/- 1.35, 1.43 +/- 0.95, 1.22 +/- 0.99; 17.1 +/- 5.0, 17.2 +/- 6.1, 19.2 +/- 8.0, respectively. At the end of the 24-months follow-up, all observed parameters had a little improvement except the average prostate volume in this group. Of the 61 patients, 42 (62%) progressed slowly or became better when comparing with baseline data of the study. Moreover, the difference between at 24-month and at baseline period, IPSS showed statistical significance (P < 0.0001) in t test. In the study of BPH progression risk factors by logistic regression analysis, prostate volume (P = 0.0910) and residual urine volume (P = 0.0780) showed a trend of becoming the risk factors. CONCLUSION: Our study showed that patients treated with watchful waiting had slow progression and majority of these patients did not need to alter their treatment options. Through data analysis, we noticed that the changes of data watchful waiting patients could help us to choose more precise and reasonable treatment option in clinical practice.

[Transperitoneal laparoscopic adrenalectomy: surgical approach and outcome].

OBJECTIVE: To investigate the efficiency and safety of transperitoneal laparoscopic adrenalectomy for the treatment of adrenal tumors and to describe surgical technique and management of intraoperative complications. METHODS: From February 2002 to April 2008, 24 male and 44 female consecutive patients with average age (53.4 +/- 12.1) years old were treated with transperitoneal laparoscopic adrenalectomy because of adrenal tumors. Of the patients, 27 cases had right adrenal tumors, 39 cases had left adrenal tumors and 2 cases had bilateral adrenal tumors. The average tumor size was (2.9 +/- 2.0) cm with the maximal diameter of 10 cm. We evaluated this technique in respect of operating time, estimated blood loss, complications during surgery, postoperative complications, duration of hospital stay and pathological results. RESULTS: All the surgeries had been completed successfully without conversion to open surgery. The average operating time was (157.7 +/- 51.5) min, the average estimated blood loss was (68.1 +/- 54.2) ml. No major complication happened during operation. The average drainage time was (2.6 +/- 1.5) days. The average post-operative hospital stay was (8.7 +/- 4.3) days. Four cases (6.0%) developed surgical field liquefaction and 2 cases (2.9%) experienced delayed closure of the drainage wound. CONCLUSIONS: Transperitoneal laparoscopic adrenalectomy is feasible and safe in the treatment of adrenal tumor with low risk of intra-operative and post-operative complication.

[Detection of urological and male genital tumors diagnosed in Beijing Hospital 1995 - 2004].

OBJECTIVE: To investigate the diagnostic condition of urological and male genital tumors in Beijing Hospital during the period 1995 - 2004. METHODS: The clinical data of 1245 patients diagnosed as with urological and male genital tumors that were hospitalized in the Department of Urology, Beijing Hospital from 1 January 1995 to 31 December 2004, 957 males and 288 females, were analyzed retrospectively. RESULTS: The 1245 with urological and male genital tumors accounted for 20.96% of the patients hospitalized in the Department of Urology of this hospital in the same period. The commonest malignancies included transitional cell carcinoma of bladder (n = 387), carcinoma of prostate (n = 271), and clear cell carcinoma of kidney (n = 250). The detected numbers of cases of these three kinds of malignancies increased year by year. The ratio of metastatic carcinoma in prostate and kidney decreased with each passing year. Before 1999 75.48% of the patients with prostate carcinoma visited the hospital because of low urinary tract symptom (LUTS), and only 12.48% because of abnormalities discovered during physical examination, However, after 2000 the percentage of the prostate carcinoma patients who visited the hospital because of LUST deceased to 54.44%, and those because of abnormalities discovered during physical examination increased to 40.99% (P < 0.01). CONCLUSION: The improvement of diagnostic methods has changed the condition of tumor diagnosis in recent years.