Behavior of Au Nanoparticles under Pressure Observed by In Situ Small-Angle X-ray Scattering.

The mechanical properties and stability of metal nanoparticle colloids under high-pressure conditions are investigated by means of optical extinction spectroscopy and small-angle X-ray scattering (SAXS), for colloidal dispersions of gold nanorods and gold nanospheres. SAXS allows us to follow in situ the structural evolution of the nanoparticles induced by pressure, regarding both nanoparticle size and shape (form factor) and their aggregation through the interparticle correlation function S(q) (structure factor). The observed behavior changes under hydrostatic and nonhydrostatic conditions are discussed in terms of liquid solidification processes yielding nanoparticle aggregation. We show that pressure-induced diffusion and aggregation of gold nanorods take place after solidification of the solvent. The effect of nanoparticle shape on the aggregation process is additionally discussed.

Anoxic desulphurisation of biogas from full-scale anaerobic digesters in suspended biomass bioreactors valorising previously nitrified digestate centrate.

Nitrification of centrate from anaerobic sewage sludge digestion presents a major opportunity as an electron acceptor in anoxic biogas biodesulphurisation. Nitritation and nitrification inhibition by free ammonia was detected at laboratory scale, but was avoided during the scale-up operation in a 4 m3 reactor treating ammonium loads up to 19 gN m-3 h-1. This nitrate-rich stream was fed to two pilot-scale suspended biomass bioreactors (SBBs) treating real biogas for 220 days. After an adaptation period of 21 days, nitrate and alkalinity concentrations in the liquid medium below 10 mgN L-1 and 100 mgCaCO3 L-1 were found to limit hydrogen sulphide (H2S) oxidation. Once controlled, 95% of the H2S was removed in SBB1 and 90% in SBB2, at a gas residence time (GRT) of 5.9 min, treating average values of 321 ± 205 ppmv and 457 ± 205 ppmv, respectively. Outlet H2S concentrations of 16 ± 24 ppmv in SBB1 and 46 ± 39 ppmv in SBB2 were obtained, which are below the requirements of biogas combustion heat and power engines. Unlike H2S, siloxanes were not removed with these GRTs. The results demonstrate the feasibility of the combined process for H2S treatment, potential valorisation of precipitated elemental sulphur and a reduction in the reagents currently used to control H2S.

On the Stiffness of Gold at the Nanoscale.

The density and compressibility of nanoscale gold (both nanospheres and nanorods) and microscale gold (bulk) were simultaneously studied by X-ray diffraction with synchrotron radiation up to 30 GPa. Colloidal stability (aggregation state and nanoparticle shape and size) in both hydrostatic and nonhydrostatic regions was monitored by small-angle X-ray scattering. We demonstrate that nonhydrostatic effects due to solvent solidification had a negligible influence on the stability of the nanoparticles. Conversely, nonhydrostatic effects produced axial stresses on the nanoparticle up to a factor 10× higher than those on the bulk metal. Working under hydrostatic conditions (liquid solution), we determined the equation of state of individual nanoparticles. From the values of the lattice parameter and bulk modulus, we found that gold nanoparticles are slightly denser (0.3%) and stiffer (2%) than bulk gold: V0 = 67.65(3) Å3, K0 = 170(3)GPa, at zero pressure.

Monodisperse Gold Nanorods for High-Pressure Refractive Index Sensing.

The effects of hydrostatic pressure on the surface plasmon resonances (SPRs) of aqueous dispersions of monodisperse gold nanorods (AuNRs) were determined up to 9 GPa. The ultranarrow longitudinal SPR band of monodisperse AuNRs allows us to monitor a gradual red shift with pressure, which shows abrupt jumps at the liquid to ice phase VI and ice phase VII transitions. Despite solidifying at low pressure (∼1.8 GPa), water displays a regime of quasi-hydrostaticity in said phases VI and VII, up to ca. 5 GPa. Above this pressure, nonhydrostatic effects manifest themselves through broadening of the SPR bands, but barely any effect is observed on the position of the surface plasmon mode. The variation in the SPR peak wavelength with pressure allowed us to determine the pressure dependence of the refractive index of water. Unlike Brillouin scattering or interferometric techniques, this plasmon-spectroscopy-based method leads to a more direct determination of the refractive index, which is well described empirically by Murnaghan-type equations in the three explored phases. We report herein the obtained analytical functions providing the pressure dependence of refractive index in the liquid, ice VI, and ice VII phases of water.

Effects of Hydrostatic Pressure on the Surface Plasmon Resonance of Gold Nanocrystals.

The surface plasmon resonances of gold nanospheres and nanorods have been measured as a function of hydrostatic pressure up to 17 GPa in methanol-ethanol 4:1 solvent and up to 10 GPa in paraffin. Both the sphere resonance and the longitudinal rod resonance exhibit redshifts, whereas the transverse rod mode shows an extremely weak redshift or blueshift depending on the nanorod aspect ratio. Solidification of the solvent around 11 GPa causes some aggregation of the particles, readily identified through broadening of the surface plasmon band and further redshifting. Spectra collected during loading and unloading cycles exhibit only minimal hysteresis if the pressure remains below 11 GPa. The surface plasmon shifts are the result of two competing effects. Compression of the conduction electrons in the metals increases the bulk plasma frequency, which causes a blueshift. However, the increase in the solvent density under hydrostatic load leads to an increase in the solvent refractive index, which in turn leads to a redshift. We find that after accounting for the solvent contribution, we can spectroscopically determine the bulk modulus of the gold nanoparticles with a precision of 10%. The value obtained of K0 = 190 GPa is significantly higher than the value for bulk gold (167 GPa). Furthermore, we show that pressure-induced solidification causes a significant broadening and anomalous shift of the surface plasmon band that we attribute to aggregation and nanorod deformation.

Descripción de un caso y revisión de la bibliografía / Transoral decompression of the brain stem in a basilar impression secondary to rheumatoid arthritis. Description of a case and survey of the literature

Introducción. La subluxación vertical o traslocación odontoidea que produce una impresión basilar con compresión del tronco cerebral es un fenómeno evolutivo último de la artritis reumatoidea; la aparición de síntomas medulares y de pares bajos es un signo específico de dicha alteración. En esta situación, los objetivos quirúrgicos establecidos son la descompresión de las estructuras nerviosas afectadas seguida de una estabilización craneocervical. El objeto de este artículo es dar a conocer la mejoría del déficit neurológico tras una cirugía transoral descompresiva (odontoidectomía), sin asociar ningún sistema de fijación interna en una paciente con artritis reumatoide de larga evolución y compresión anterior del tronco cerebral por impresión basilar y panus reumatoideo. Tras revisar la literatura, no existe, excepto algún caso clínico aislado, ningún artículo donde se describa la evolución postoperatoria de la descompresión quirúrgica por vía anterior del tronco cerebral en pacientes con subluxación odontoidea reumatoidea, sin asociar ningún sistema de estabilización interna. Caso clínico. Mujer de 65 años de edad, diagnosticada de artritis reumatoide a los 25 años, que ingresa con síntomas de compresión bulbomedular secundarios a una subluxación vertical de odontoides. Se le practicó una descompresión transoral del tronco cerebral(odontoidectomía y extirpación de pannus sin fijación posterior), con una evolución postoperatoria sorprendentemente favorable. Realizó una vida independiente a los 15 meses de la descompresión quirúrgica. Conclusiones. La mejoría neurológica de nuestra enferma tras la odontoidectomía descompresiva sugiere que la compresión mecánica de la odontoides impactada en el tronco cerebral fue el factor etiológico predominante de los síntomas bulbomedulares, mientras que su estabilización clínica puede explicarse por un mecanismo de autofusión espontánea de las masas laterales del atlas con los cóndilos occipitales y con el axis. Finalmente, consideramos que, en casos seleccionados de pacientes reumatoideos con subluxación atloaxoidea, impactación de odontoides en foramen magno y clínica compresiva bulbomedular, la descompresión transoral del tronco cerebral mediante odontoidectomía es el procedimiento quirúrgico inicial de elección, con el que se consigue una mejoría neurológica y una estabilización clínica. En cualquier caso, es preciso un seguimiento postoperatorio neurológico y radiológico estricto ante la posibilidad futura de una fijación craneocervical (AU)

Introduction. The vertical subluxation or translocation of the odontoid process producing a basilar impression with compression of the brain stem is a late phenomenon in the course of rheumatoid arthritis; the appearance of symptoms in the spinal cord and the lower pairs of spinal nerves is a specific sign of this disorder. In this situation, the standard surgical aims are the decompression of the affected nerve structures followed by craniocervical stabilisation. The objective of this paper is to report on the improvement of the neurological deficit after decompressive transoral surgery (odontoidectomy), without associating any internal fixation system, in a female patient with a long history of rheumatoid arthritis and anterior compression of the brain stem caused by basilar impression and rheumatoid pannus. A survey of the literature showed that, with the odd isolated clinical case, there are no papers which describe the post-operative development of surgical decompression of the brain stem carried out through an anterior approach in patients with rheumatoid subluxation of the odontoid process, without associating any internal stabilisation system. Case report. Female aged 65, diagnosed as suffering from rheumatoid arthritis at the age of 25, who was admitted with symptoms of compression of the medulla oblongata secondary to a vertical subluxation of the odontoid process. She was submitted to transoral decompression of the brain stem (odontoidectomy and removal of pannus without posterior fixation), and made surprisingly favourable post-operative progress. At 15 months after the surgical decompression she led an independent life. Conclusions. The neurological improvement of our patient after the decompressive odontoidectomy suggests that the mechanical compression of the odontoid process with impaction of the brain stem was the predominant aetiological factor causing the symptoms in the medulla oblongata. Her clinical stabilisation, on the other hand, can be explained by a mechanism involving the spontaneous autofusion of the lateral masses of the atlas with the occipital condyle and with the axis. Lastly, we consider that, in certain cases of rheumatoid patients with atlantoaxial subluxation, impaction of the odontoid process in the foramen magnum and clinical features involving compression of the medulla oblongata, transoral decompression of the brain stem through an odontoidectomy is the choice initial surgical procedure, since it affords neurological improvement and clinical stabilisation. In any case, a strict neurological and radiological post-operative followup is needed in view of a possible craniocervical fixation occurring in the future (AU)

[Transoral decompression of the brain stem in a basilar impression secondary to rheumatoid arthritis. Description of a case and survey of the literature]. / Descompresion transoral del tronco cerebral en una impresion basilar secundaria a artritis reumatoidea. Descripcion de un caso y revision de la bibliografia.

INTRODUCTION: The vertical subluxation or translocation of the odontoid process producing a basilar impression with compression of the brain stem is a late phenomenon in the course of rheumatoid arthritis; the appearance of symptoms in the spinal cord and the lower pairs of spinal nerves is a specific sign of this disorder. In this situation, the standard surgical aims are the decompression of the affected nerve structures followed by craniocervical stabilisation. The objective of this paper is to report on the improvement of the neurological deficit after decompressive transoral surgery (odontoidectomy), without associating any internal fixation system, in a female patient with a long history of rheumatoid arthritis and anterior compression of the brain stem caused by basilar impression and rheumatoid pannus. A survey of the literature showed that, with the odd isolated clinical case, there are no papers which describe the post operative development of surgical decompression of the brain stem carried out through an anterior approach in patients with rheumatoid subluxation of the odontoid process, without associating any internal stabilisation system. CASE REPORT: Female aged 65, diagnosed as suffering from rheumatoid arthritis at the age of 25, who was admitted with symptoms of compression of the medulla oblongata secondary to a vertical subluxation of the odontoid process. She was submitted to transoral decompression of the brain stem (odontoidectomy and removal of pannus without posterior fixation), and made surprisingly favourable post operative progress. At 15 months after the surgical decompression she led an independent life. CONCLUSIONS: The neurological improvement of our patient after the decompressive odontoidectomy suggests that the mechanical compression of the odontoid process with impaction of the brain stem was the predominant aetiological factor causing the symptoms in the medulla oblongata. Her clinical stabilisation, on the other hand, can be explained by a mechanism involving the spontaneous autofusion of the lateral masses of the atlas with the occipital condyle and with the axis. Lastly, we consider that, in certain cases of rheumatoid patients with atlantoaxial subluxation, impaction of the odontoid process in the foramen magnum and clinical features involving compression of the medulla oblongata, transoral decompression of the brain stem through an odontoidectomy is the choice initial surgical procedure, since it affords neurological improvement and clinical stabilisation. In any case, a strict neurological and radiological post operative follow up is needed in view of a possible craniocervical fixation occurring in the future.