Analysis of Vibration Isolators for Hermetic Compressors

Nowadays, the customers of refrigerators and freezers have become more exigent in respect to the acoustic comfort of these home appliances. Among the noise sources, there are the refrigerant flow, the fans and the compressors. The compressors might be responsible for a part of the cabinet low frequency noise which could be generated either by the gas pulsation that excites the tubing or the compressor low frequency vibration that transfers energy to the cabinet base plate and tubing. The compressor low frequency vibration is a function of the mechanism loads and the gas pressure that acts on the piston and it is modulated by its running frequency and harmonics. Besides, at low frequencies, the compressor behaves as a rigid body assembled on isolators or grommets which link the compressor to the cabinet base plate. If one knows these rigid body natural frequencies, it’s possible to optimize the refrigerator project, providing a better acoustic performance for manufacturers and final customers. Based on this context, this paper aims to present a study of the compressor grommets, usually made in rubber. First of all, an investigation about the materials is carried out using a technique with a single degree-of-freedom system. In a second time, an analysis of the static behavior of an isolator using the rubber properties is done. Finally, a numerical model to predict the modal behavior of a compressor assembled on a rigid base is created and validated experimentally

Crystals on the Iris: Russell Bodies in Fuchs Uveitis

This is a Photo Essay and does not have an abstract. Please download the PDF or view the article HTML

Acoustic Improvements for a New Generation of Variable Speed Compressor

Variable speed reciprocating compressors (VSRC) present some advantages comparing to single speed compressors, mainly in terms of energy consumption and noise. Once the acoustic performance is analyzed, it is verified that the compressor running most part of the time at frequencies lower than the ones of the electric nets imply lower sound level for VSRC and, therefore, many home appliances manufacturers direct their use in the premium refrigerator models. Following a general market trend for comfort items, home appliances noise is becoming more and more important nowadays, implying even VSRCs demand acoustic improvements in order to reduce the sound level of the refrigerators. In such a scenario, this paper presents numerical and experimental studies carried out in an existing platform of variable speed compressors, identifying some sources and transmission paths associated to the overall sound level of the compressor itself and a representative refrigerator model. Based on the foreseen opportunities, a design optimization focusing on sources and paths is presented and, as a result, the acoustic performance of the new generation is compared to the performance of the current version of this variable speed compressor platform

Influence of size reduction of fly ash particles by grinding on the chemical properties of geopolymers

Chemical properties of geopolymers were evaluated from the reduction of fly ash particle size by grinding. X-ray diffraction determined that at early curing ages new crystalline phases appear in the matrix of the geopolymer and they remain for 28 days, with increases in intensities up to 60%. In Fourier transform infrared spectroscopy, displacements were identified in the main band of the geopolymers at higher wavenumbers, attributed to the greater rigidity in the structures of the aluminosilicate gel due to the increase of the reaction products in the geopolymers obtained through fly ashsubjected to previous grinding, which is observable in the geopolymers matrix. Results indicate that the reduction of fly ash particle size by grinding has an influence on the chemical properties of geopolymers.Peer ReviewedPostprint (published version

Noise Characteristics Improvements for a New Generation of Variable Capacity Compressor using Linear Motor Technology

The household appliances market noise levels requirements have rapidly increased in the last years. Despite the traditional approach for defining noise requirements focused on steady-state sound power levels, the transient noise is becoming a key factor in defining sound quality specification. Variable speed compressor technologies lead to a significant advantage on this aspect since in standard operation conditions the compressor runs at relatively low speeds for most of the time. Linear motor driven reciprocating compressors present great advantages since this technology allows dealing with cooling capacity variation without changing the motor speed. This allows also easier and more effective design of lower noise generation. This paper presents the benefits of the variable capacity, linear motor driven reciprocating compressors over rotary motor driven reciprocating compressors, either at variable capacity and fixed speeds. Emphasis is given to the physical phenomena and engineering advantages of the linear motor concept

The atlas of unburnable oil for supply-side climate policies

To limit the increase in global mean temperature to 1.5 °C, CO2 emissions must be drastically reduced. Accordingly, approximately 97%, 81%, and 71% of existing coal and conventional gas and oil resources, respectively, need to remain unburned. This article develops an integrated spatial assessment model based on estimates and locations of conventional oil resources and socio-environmental criteria to construct a global atlas of unburnable oil. The results show that biodiversity hotspots, richness centres of endemic species, natural protected areas, urban areas, and the territories of Indigenous Peoples in voluntary isolation coincide with 609 gigabarrels (Gbbl) of conventional oil resources. Since 1524 Gbbl of conventional oil resources are required to be left untapped in order to keep global warming under 1.5 °C, all of the above-mentioned socio-environmentally sensitive areas can be kept entirely off-limits to oil extraction. The model provides spatial guidelines to select unburnable fossil fuels resources while enhancing collateral socio-environmental benefits

Characterization of Mentorship Programs in Departments of Surgery in the United States

Importance Mentorship is considered a key element for career satisfaction and retention in academic surgery. Stakeholders of an effective mentorship program should include the mentor, the mentee, the department, and the institution. Objective The objective of this study was to characterize the status of mentorship programs in departments of surgery in the United States, including the roles of all 4 key stakeholders, because to our knowledge, this has never been done. Design, Setting, and Participants A survey was sent to 155 chairs of departments of surgery in the United States in July 2014 regarding the presence and structure of the mentorship program in their department. The analysis of the data was performed in November 2014 and December 2014. Main Outcomes and Measures Presence and structure of a mentorship program and involvement of the 4 key stakeholders. Results Seventy-six of 155 chairs responded to the survey, resulting in a 49% response rate. Forty-one of 76 of department chairs (54%) self-reported having an established mentorship program. Twenty-five of 76 departments (33%) described no formal or informal pairing of mentors with mentees. In 62 (82%) and 59 (78%) departments, no formal training existed for mentors or mentees, respectively. In 42 departments (55%), there was no formal requirement for the frequency of scheduled meetings between the mentor and mentee. In most departments, mentors and mentees were not required to fill out evaluation forms, but when they did, 28 of 31 were reviewed by the chair (90%). In 70 departments (92%), no exit strategy existed for failed mentor-mentee relationships. In more than two-thirds of departments, faculty mentoring efforts were not recognized formally by either the department or the institution, and only 2 departments (3%) received economic support for the mentoring program from the institution. Conclusions and Relevance These data show that only half of departments of surgery in the United States have established mentorship programs, and most are informal, unstructured, and do not involve all of the key stakeholders. Given the importance of mentorship to career satisfaction and retention, development of formal mentorship programs should be considered for all academic departments of surgery

Shape Optimization of a Compressor Supporting Plate Based on Vibration Modes

In typical household refrigeration systems, the compressor is structurally connected to the cabinet through an assembly composed of rubber mounts and a steel support plate, usually called base-plate. This plate works as a vibration energy path from the compressor to other refrigerator components, and its dynamic behavior must be known in order to avoid the coincidence of resonances and operational frequencies , a situation in which the energy flow is maximized. One way to design a support that satisfies this requirement is to optimize the shape of the plate, locating its structural modes as far as possible from the operational frequency and first harmonics. In this work, the Finite Element Method (FEM) is used to solve the eigenvalue problem and to parameterize the optimization procedure, which is based on positioning of the nodes of a design region (the plate) in a FEM simplified model. Due to the large number of variables, a gradient-based method is adopted. The objective of the methodology is to maximize the difference between two adjacent eigenvalues near the fundamental operation frequency of the compressor, in order to obtain a large and effective bandgap. A geometrical constraint is imposed to the problem and it is represented by a maximum allowed deformation of the plate. The gradients needed are obtained using elementary stiffness and mass matrices information. The obtained results show that the procedure leads to a new shape which ensures the desired dynamic characteristics for the support plate

Loss of MECP2 Leads to Activation of P53 and Neuronal Senescence.

To determine the role for mutations of MECP2 in Rett syndrome, we generated isogenic lines of human induced pluripotent stem cells, neural progenitor cells, and neurons from patient fibroblasts with and without MECP2 expression in an attempt to recapitulate disease phenotypes in vitro. Molecular profiling uncovered neuronal-specific gene expression changes, including induction of a senescence-associated secretory phenotype (SASP) program. Patient-derived neurons made without MECP2 showed signs of stress, including induction of P53, and senescence. The induction of P53 appeared to affect dendritic branching in Rett neurons, as P53 inhibition restored dendritic complexity. The induction of P53 targets was also detectable in analyses of human Rett patient brain, suggesting that this disease-in-a-dish model can provide relevant insights into the human disorder

Dinâmica da vegetação em pastagem nativa, submetida a diferentes métodos de controle de espécies indesejáveis e adubaçãoVegetation dynamics in native pasture submitted to control methods for weeds species and fertilization

Em área de pastagem nativa representativa da transição entre a Serra do Sudeste e a Depressão Central do Rio Grande do Sul, foram testados os efeitos associativos de quatro métodos de controle de plantas indesejáveis 1 - sem controle (SC); 2 - controle mecânico - roçada de primavera (CMP); 3 - controle mecânico - roçada de outono (CMO) e 4 - controle químico - herbicida comercial a base de Picloram (64 g.l-1) + 2,4-D (240 g.l-1), na dosagem de 5 l p.c.ha-1 (CQT)), dois sistemas de fertilização (1 - sem-adubo e 2 - com adubo), duas datas de avaliação (1 - primeira data - 16/05/2003 e 2 - segunda data - 26/03/2004 ) e dois toques na pastagem (1 - estrato superior e 2 - estrato inferior) sobre a composição florística e freqüência de espécies. As leguminosas nativas ocupam, com maior frequência, o estrato inferior da pastagem (5,9%), as indesejáveis, ao contrário das leguminosas, ocupam o estrato superior (5%). O controle químico proporcionou aumento na frequência de gramíneas à medida que diminuiu a participação de leguminosas. A gramínea com maior participação na composição da pastagem foi o Paspalum notatum com diminuição especialmente de Desmodium incanum dentre as leguminosas no CQT. A adubação favoreceu a participação da leguminosa Trifolium polymorphum (2,0% vs 1,1%, com adubação e sem-adubação, respectivamente). O controle mecânico proporcionou aumento na frequência de Vernonia nudiflora no estrato inferior (5,7%) da pastagem comparando-se ao SC (3,6%). O controle mecânico de outono, com apenas uma roçada durante o período experimental, foi mais eficiente que o mecânico de primavera.Abstract In a representative natural pasture area in the transition between the Serra do Sudeste and Depressão Central in Rio Grande do Sul, the associated effects of four methods for controlling undesirable species were tested (1 = without control (SC), 2 = mechanical control – spring mowing (CMP), 3 = mechanical control – autumn mowing (CMO) and 4 = chemical control – commercial herbicide Tordon, composed by Picloram (64 g.l-1) + 2,4-D (240 g.l-1), in the dosage of 5 l p.c.ha-1 (CQT)), associated to two systems of fertilization ( 1 = without fertilizer and 2 = with fertilizer). Two evaluation times (05/16/03 and 03/26/04) and two touch in pasture (1 = first touch and 2 = second touch) were considered on aspects related to the floristic survey and species frequency. The native leguminous plants generally appear in the lower stratus of the pasture (5.9 %), the undesirable ones appear in the upper stratus (5.0%). The chemical control promoted an increase in the grass frequency, as well as decreased the leguminous presence. The Paspalum notatum is the most frequent grass, and Desmodium incanum, mainly, decreased (among the legumes) in CQT. The fertilization favored the Trifolium polymorphum participation (2.0% vs 1.1% with and without fertilization, respectively). The mechanical control increased the frequency of Vernonia nudiflora in lower pasture stratus (5.7%) comparing to SC (3.6%). The autumn mechanical control with only one application during the experience time was more effi cient than the spring mechanical control