On the Importance of Frictional Energy Dissipation in the Prevention of Undesirable Self-Excited Vibrations in Gas Foil Bearing Rotor Systems

In this contribution, a nonlinear and fully coupled fluid–structure–rotor interaction model of a gas foil bearing rotor system is presented. Aiming at the reduction of undesirable self-excited vibrations, many common bearing designs feature a compliant and slightly movable multi-part foil structure inside the lubrication gap. The present paper discusses the general impact of frictional energy dissipation within the foil structure by adding equivalent viscous damping to the widespread simple elastic foundation model. For the computational analysis, the PDEs describing the fluid pressure distribution and the foil structure deformation field are spatially discretized using finite difference schemes. After suitable nondimensionalization of the resulting system of nonlinear ODEs, a corresponding state-space representation is deduced. Using numerical simulation tools, the stability of equilibrium points and the occurrence of self-excited vibrations are addressed and possible bifurcation scenarios are discussed. Summing up all results, frictional energy dissipation proves to be of crucial importance with regard to the reduction or prevention of undesirable self-excited vibrations in gas foil bearing rotor systems

Band structure of helimagnons in MnSi resolved by inelastic neutron scattering

A magnetic helix realizes a one-dimensional magnetic crystal with a period given by the pitch length $\lambda_h$. Its spin-wave excitations -- the helimagnons -- experience Bragg scattering off this periodicity leading to gaps in the spectrum that inhibit their propagation along the pitch direction. Using high-resolution inelastic neutron scattering the resulting band structure of helimagnons was resolved by preparing a single crystal of MnSi in a single magnetic-helix domain. At least five helimagnon bands could be identified that cover the crossover from flat bands at low energies with helimagnons basically localized along the pitch direction to dispersing bands at higher energies. In the low-energy limit, we find the helimagnon spectrum to be determined by a universal, parameter-free theory. Taking into account corrections to this low-energy theory, quantitative agreement is obtained in the entire energy range studied with the help of a single fitting parameter.Comment: 5 pages, 3 figures; (v2) slight modifications, published versio

Thickness-dependent spontaneous dewetting morphology of ultrathin Ag films

We show here that the morphological pathway of spontaneous dewetting of ultrathin Ag films on SiO2 under nanosecond laser melting is found to be film thickness dependent. For films with thickness h between 2 <= h <= 9.5 nm, the morphology during the intermediate stages of dewetting consisted of bicontinuous structures. For films 11.5 <= h <= 20 nm, the intermediate stages consisted of regularly-sized holes. Measurement of the characteristic length scales for different stages of dewetting as a function of film thickness showed a systematic increase, which is consistent with the spinodal dewetting instability over the entire thickness range investigated. This change in morphology with thickness is consistent with observations made previously for polymer films [A. Sharma et al, Phys. Rev. Lett., v81, pp3463 (1998); R. Seemann et al, J. Phys. Cond. Matt., v13, pp4925, (2001)]. Based on the behavior of free energy curvature that incorporates intermolecular forces, we have estimated the morphological transition thickness for the intermolecular forces for Ag on SiO2 . The theory predictions agree well with observations for Ag. These results show that it is possible to form a variety of complex Ag nanomorphologies in a consistent manner, which could be useful in optical applications of Ag surfaces, such as in surface enhanced Raman sensing.Comment: 20 pages, 5 figure

Root cortex development is fine-tuned by the interplay of MIGs, SCL3 and DELLAs during arbuscular mycorrhizal symbiosis

Root development is a crucial process that determines the ability of plants to acquire nutrients, adapt to the substrate and withstand changing environmental conditions. Root plasticity is controlled by a plethora of transcriptional regulators that allow, in contrast to tissue development in animals, post-embryonic changes that give rise to new tissue and specialized cells. One of these changes is the accommodation in the cortex of hyperbranched hyphae of symbiotic arbuscular mycorrhizal (AM) fungi, called arbuscules. Arbuscule-containing cells undergo massive reprogramming to coordinate developmental changes with transport processes. Here we describe a novel negative regulator of arbuscule development, MIG3. MIG3 induces and interacts with SCL3, both of which modulate the activity of the central regulator DELLA, restraining cortical cell growth. As in a tug-of-war, MIG3-SCL3 antagonizes the function of the complex MIG1-DELLA, which promotes the cell expansion required for arbuscule development, adjusting cell size during the dynamic processes of the arbuscule life cycle. Our results in the legume plant Medicago truncatula advance the knowledge of root development in dicot plants, showing the existence of additional regulatory elements not present in Arabidopsis that fine-tune the activity of conserved central modules

Associations Between Presenting Symptoms, Clinicopathological Parameters, and Prognosis in a Contemporary Series of Patients With Renal Cell Carcinoma

PURPOSE: To evaluate the impact of presenting symptoms on survival in a contemporary series of patients with renal cell carcinoma (RCC). MATERIALS AND METHODS: We prospectively recorded data on the presenting symptoms, pathology, and RCC-specific survival of 633 consecutive RCC patients who underwent surgery between 2003 and 2012. RESULTS: Four hundred thirty-three RCCs (68%) were incidental, 111 (18%) were associated with local symptoms, and 89 (14%) were associated with systemic symptoms. Among those with incidental RCC, 317 patients (73%) were completely asymptomatic and 116 patients (27%) presented with symptoms not related to the tumor. During a median follow-up interval of 40 months (interquartile range: 39 to 69 months), 77 patients died from RCC. In univariate analyses, symptom classification was significantly associated with RCC-specific survival (p&lt;0.001). Patients with incidental RCC and unrelated symptoms tended to have worse prognosis than did patients who were completely asymptomatic, although this difference was not statistically significant (p=0.057). The symptom classification was associated with advanced TNM stages (p&lt;0.001) and grade (p&lt;0.001). CONCLUSIONS: This study confirms that presenting symptoms are associated with tumor characteristics and survival. The majority of RCCs are diagnosed incidentally in patients without any symptoms or with symptoms not related to RCC. Patients in the latter group tend to have a worse prognosis than do patients who are completely asymptomatic. With the increasing number of incidentally diagnosed RCCs, substratification of patients with incidental tumors may be prognostically relevant

Dewetting of thin polymer films near the glass transition

Dewetting of ultra-thin polymer films near the glass transition exhibits unexpected front morphologies [G. Reiter, Phys. Rev. Lett., 87, 186101 (2001)]. We present here the first theoretical attempt to understand these features, focusing on the shear-thinning behaviour of these films. We analyse the profile of the dewetting film, and characterize the time evolution of the dry region radius, $R_{d}(t)$, and of the rim height, $h_{m}(t)$. After a transient time depending on the initial thickness, $h_{m}(t)$ grows like $\sqrt{t}$ while $R_{d}(t)$ increases like $\exp{(\sqrt{t})}$. Different regimes of growth are expected, depending on the initial film thickness and experimental time range.Comment: 4 pages, 5 figures Revised version, published in Physical Review Letters: F. Saulnier, E. Raphael and P.-G. de Gennes, Phys. Rev. Lett. 88, 196101 (2002