Metal films of nanoscale thickness, deposited on substrates and exposed to laser heating, provide systems that involve several interesting multiphysics effects. In addition to fluid mechanical ...aspects associated with a free boundary setup, other relevant physical effects include phase change, thermal flow, and liquid-solid interactions. Such films are challenging to model, in particular because inertial effects may be relevant, and large contact angles require care when considering the long-wave formulation. Applications of nanoscale metal films are numerous, and the materials science community is actively pursuing more complex setups involving templated films and substrates, bimetallic films and alloys, and a variety of elemental film geometries. The goal of this review is to discuss our current understanding of thin metal film systems, while also providing an overview of the challenges in this research area, which stands at the intersection of fluid mechanics, materials science, and thermal physics.
We consider the coupled process of phase separation and dewetting of metal alloys of nanoscale thickness deposited on solid substrates. The experiments involve applying nanosecond laser pulses that ...melt the Ag40Ni60 alloy films in two setups: either on thin supporting membranes or on bulk substrates. These two setups allow for extracting both temporal and spatial scales on which the considered processes occur. The theoretical model involves a longwave version of the Cahn–Hilliard formulation used to describe spinodal decomposition, coupled with an asymptotically consistent longwave-based description of dewetting that occurs due to destabilizing interactions between the alloy and the substrate, modeled using the disjoining pressure approach. Careful modeling, combined with linear stability analysis and fully nonlinear simulations, leads to results consistent with the experiments. In particular, we find that the two instability mechanisms occur concurrently, with the phase separation occurring faster and on shorter temporal scales. The modeling results show a strong influence of the temperature dependence of relevant material properties, implying that such a dependence is crucial for the understanding of the experimental findings. The agreement between theory and experiment suggests the utility of the proposed theoretical approach in helping to develop further experiments directed toward formation of metallic alloy nanoparticles of desired properties.
Nanolithographically patterned copper rings were synthesized, and the self-assembly of the rings into ordered nanoparticle/nanodrop arrays was accomplished via nanosecond pulsed laser heating above ...the melt threshold. The resultant length scale was correlated to the transport and instability growths that occur during the liquid lifetime of the melted copper rings. For 13-nm-thick rings, a change in the nanoparticle spacing with the ring width is attributed to a transition from a Raleigh−Plateau instability to a thin film instability because of competition between the cumulative transport and instability timescales. To explore the competition between instability mechanisms further, we carried out experiments with 7-nm-thick rings. In agreement with the theoretical predictions, these rings break up in both the azimuthal and radial directions, confirming that a simple hydrodynamic model captures the main features of the processes leading to the breakup.
ABSTRACT
The aim of the present study was to gain insight into the pathophysiology of obesity by comparing the pattern of gene expression of omental adipose tissue of obese and lean volunteers using ...DNA microarrays. Omental adipose tissue biopsies were obtained by laparoscopic surgery from six male patients (44.2±6.3 yr). RNA was extracted and pooled for the obese (BMI: 37.3±2.5 kg/m2) and lean (BMI: 23.4±0.8 kg/m2) groups. From the total number of genes analyzed (1,152 well‐characterized human genes), 41% were expressed at sufficient levels in human adipose tissue for detection in the microarray experiments, finding that 89 genes were up‐ regulated while 64 were down‐regulated at least twofold in the omental adipose tissue obtained from obese patients. We found a general tendency to blunt lipolysis inducer genes and a global down‐regulation of genes encoding growth factors. Moreover, an up‐regulation in the expression of several mitogen‐activated protein kinases (MAPKs) was observed. The down‐regulation of genes involved in lipolysis activation may be involved in the etiopathogenesis of obesity. In addition, down‐regulation of growth factors and the up‐regulation of MAPKs may indicate an attempt to restrain adipocyte proliferation and differentiation. Furthermore, obesity is accompanied by an altered expression in omental adipose tissue of genes involved not only in energy homeostasis but also in quite diverse biological functions, such as immune response. The genomic approach underlines the importance of adipose tissue beyond energy metabolism.
Background
Latero-lateral duodenojejunostomy is the treatment of choice for superior mesenteric artery syndrome (SMAS). The present study analyzes the long-term outcomes in 13 patients undergoing ...laparoscopic surgery for SMAS.
Materials and methods
A retrospective study of 10 females and three males undergoing surgery between 2001 and 2013 was performed. Demographic, clinical and radiologic data and long-term surgical outcomes were recorded. In 12 patients latero-lateral duodenojejunostomy and in one patient distal laparoscopic gastrectomy with Roux-en-Y reconstruction were performed. The median age was 24 years (20–28), and the median duration of symptoms was 24 months (5–24). The most frequent symptoms were abdominal pain (
n
= 11; 92.3%), nausea and vomiting (
n
= 10; 77%) and weight loss (
n
= 9; 69.2%). The median operating time was 98 min (86–138) and hospital stay was 3 days (1–14).
Results
No reconversions occurred, and one patient experienced gastric emptying delay in the immediate postoperative period with spontaneous resolution. In four patients, SMAS was associated with severe stenosis of the celiac trunk which was treated in the same operation, and four patients presented stenosis of the left renal vein (the “nutcracker” phenomenon). With a median follow-up of 94 months (SD 65.3), eight patients (61.5%) had excellent results. One patient had a relapse of symptoms 4 years after surgery requiring distal gastrectomy, two patients presented delay in gastric emptying following temporary improvement and one patient experienced no improvement.
Conclusions
Latero-lateral duodenojejunostomy yields good results in SMAS although it requires other gastric motility disorders to be ruled out for appropriate treatment to be established.
We study the instability of nanometric Cu thin films on SiO2 substrates. The metal is melted by means of laser pulses for some tens of nanoseconds, and during the liquid lifetime, the free surface ...destabilizes, leading to the formation of holes at first and then in later stages of the instability to metal drops on the substrate. By analyzing the Fourier transforms of the SEM (scanning electron microscope) images obtained at different stages of the metal film evolution, we determine the emerging length scales at relevant stages of the instability development. The results are then discussed within the framework of a long-wave model. We find that the results may differ whether early or final stages of the instability are considered. On the basis of the interpretation of the experimental results, we discuss the influence of the parameters describing the interaction of the liquid metal with the solid substrate. By considering both the dependence of dominant length scales on the film thickness and the measured contact angle, we isolate a model which predicts well the trends found in the experimental data.
Background
Laparoscopic arcuate ligament release has been demonstrated a valid therapeutic option for arcuate ligament syndrome. Nevertheless, long-term follow-up and predictive factors have not been ...described for this treatment.
Methods
Clinical and surgical data and short- and long-term outcomes together with the impact of the degree of stenosis of the celiac trunk were analyzed in 13 consecutive patients who underwent laparoscopic arcuate ligament release between 2001 and 2013.
Results
Thirteen patients (12 F/1 M) underwent surgery. The median age was 32 years old, and their mean body mass index was 20.7 (range 14.7–25). The 13 patients presented with intense postprandial abdominal pain. Ten cases were associated with weight loss. The median duration of symptoms was 24 months (range 2–240). Three patients presented symptoms associated with superior mesenteric artery syndrome. Median operative time was 120 min (range 90–240), and there were no conversions to open surgery. Median hospital stay was 3 days (range 2–14). Over a median follow-up of 117 months (range 45–185), nine patients had excellent results although two required endovascular procedures at 70 and 24 months after surgery. Four patients (30.7%) experienced poor outcomes. When we analyzed the impact of the degree of occlusion of the celiac trunk, we observed that in patients with severe occlusion (> 70%), better results were obtained, with complete resolution of symptoms in 71% of cases.
Conclusion
Laparoscopic arcuate ligament release constitutes an excellent treatment for arcuate ligament syndrome. The degree of occlusion of the celiac trunk may be a factor predictive of long-term outcomes.
Occipital nerve stimulation (ONS) is a surgical treatment proposed for drug-resistant chronic cluster headache (drCCH). Long-term series assessing its efficacy are scarce. We designed a retrospective ...observational study with consecutive sampling, evaluating the follow-up of 17 drCCH patients who underwent ONS. Our main endpoint was the reduction the rate of attacks per week. We also evaluated the pain intensity through the Visual Analogue Scale (VAS), patient overall perceived improvement and decrease in oral medication intake. After a median follow-up of 6.0 years (4.5-9.0), patients decreased from a median of 30 weekly attacks to 22.5 (5.6-37.5,
= 0.012), 7.5 at 1 year (
= 0.006) and 15.0 at the end of follow-up (
= 0.041). The VAS decreased from a median of 10.0 to 8.0 (
= 0.011) at three months, to 7.0 (
= 0.008) at twelve months and 7.0 (
= 0.003) at the end of the follow-up. A total of 23.5% had an overall perceived improvement of ≥70% at 3 months, 41.2% at 1 year and 27.8% at the end of follow-up. Reducing prophylactic oral medication was possible in 76.5% and it was stopped in 17.7%. Triptan use decreased in all the responder patients and 17.7% stopped its intake. A total of 41.2% presented mild adverse events. In conclusion, our long-term experience suggests that ONS could be an interesting option for drCCH-selected patients, as it is a beneficial and minimally invasive procedure with no serious adverse events.
We consider nanometer-sized fluid annuli (rings) deposited on a solid substrate and ask whether these rings break up into droplets due to the instability of Rayleigh-Plateau-type modified by the ...presence of the substrate, or collapse to a central drop due to the presence of azimuthal curvature. The analysis is carried out by a combination of atomistic molecular dynamics simulations and a continuum model based on a long-wave limit of Navier–Stokes equations. We find consistent results between the two approaches, and demonstrate characteristic dimension regimes which dictate the assembly dynamics.
We study the effects of stochastic thermal fluctuations on the instability of the free surface of a flat liquid metallic film on a solid substrate. These fluctuations are represented by a stochastic ...noise term added to the deterministic equation for the film thickness within the long-wave approximation. Unlike the case of polymeric films, we find that this noise, while remaining white in time, must be colored in space, at least in some regimes. The corresponding noise term is characterized by a nonzero correlation length, ℓ_{c}, which, combined with the size of the system, leads to a dimensionless parameter β that accounts for the relative importance of the spatial correlation (β∼ℓ_{c}^{-1}). We perform the linear stability analysis (LSA) of the film both with and without the noise term and find that for ℓ_{c} larger than some critical value (depending on the system size), the wavelength of the peak of the spectrum is larger than that corresponding to the deterministic case, while for smaller ℓ_{c} this peak corresponds to smaller wavelength than the latter. Interestingly, whatever the value of ℓ_{c}, the peak always approaches the deterministic one for larger times. We compare LSA results with the numerical simulations of the complete nonlinear problem and find a good agreement in the power spectra for early times at different values of β. For late times, we find that the stochastic LSA predicts well the position of the dominant wavelength, showing that nonlinear interactions do not modify the trends of the early linear stages. Finally, we fit the theoretical spectra to experimental data from a nanometric laser-melted copper film and find that at later times, the adjustment requires smaller values of β (larger space correlations).
PDF
