bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between Intraoperative Cultures during Hip Arthroplasty, Obesity, and the Risk of Early Prosthetic Joint Infection: A Prospective Study of 428 Patients
Authors: Font-Vizcarra Lluís , Tornero Eduard , Bori Guillem , Bosch Jordi , Mensa Josep , Soriano Alex
Published: November 2011

Purpose

To evaluate the relationship between intraoperative cultures during hip arthroplasty, the different patient characteristics, and the risk of developing a prosthetic joint infection (PJI).

Methods

A prospective observational study was performed. Patients who underwent elective THA from March 2007 to March of 2011 were included. Three samples were taken just after arthrotomy: synovial fluid inoculated into blood culture flasks (SF), a tissue sample (TS), and a swab of periprosthetic tissue (S). Patients received standard antibiotic prophylaxis. The PJI rate within the first 3 months after arthroplasty was recorded.

Results

402 prostheses were included in the study. Contamination rate of synovial fluid was 10.2%. The most frequent isolated microorganism was coagulase-negative staphylococci (CoNS) (32 out of 41). Body mass index (BMI) was the only host characteristic associated with positive intraoperative culture (p=0.009). The PJI rate was 3.7%. Variables associated with PJI in the univariate and multivariate analysis were: age ≥67 years (p=0.012 OR: 5.35 (1.45–19.81); CI95%) and a BMI ≥35 (p=0.002, OR: 7.7 (2.12–27.85) CI95%). PJI rate among patients with BMI<35 with negative and positive intraoperative cultures was 3% and 2.7%, respectively, however, the rate among patients with BMI ≥ 35 was 15% and 25%, respectively.

Conclusion

A BMI ≥35 was associated with a higher risk of positive intraoperative culture during hip arthroplasty. In addition, a BMI ≥35 was independently associated with a high risk of PJI and the highest rate was documented among obese patients with positive intraoperative cultures.
Antibiotic-Induced Biofilm Formation
Authors: Kaplan Jeffrey B.
Published: November 2011

Surface-attached colonies of bacteria known as biofilms play a major role in the pathogenesis of device-related infections. Biofilm colonies are notorious for their resistance to suprainhibitory concentrations of antibiotics. Numerous studies have shown that subminimal inhibitory concentrations of some antibiotics can act as agonists of bacterial biofilm formation in vitro, a process that may have clinical relevance. This article reviews studies demonstrating that low-dose antibiotics induce bacterial biofilm formation. These studies have provided important information about the regulation of biofilm formation and the signaling pathways involved in global gene regulation in response to cell stressors. It is still unclear whether antibiotic-induced biofilm formation contributes to the inconsistent success of antimicrobial therapy for device infections.
Biofilm Formation of Candida spp. Isolates from Patients at a Cardiothoracic Intensive Care Unit
Authors: Tobudic Selma , Kratzer Christina , Lassnigg Andrea , Willinger Birgit , Graninger Wolfgang , Presterl Elisabeth
Published: November 2011

Invasive Candida infections in seriously ill patients are rare but associated with high mortality, while Candida colonization of the mucocuteneous surfaces is common in patients admitted to intensive care units. To investigate biofilm formation as a possible virulence factor, we analyzed the biofilm formation of 128 non-invasive isolates from long-term ICU patients and that of 106 invasive bloodstream isolates. Candida biofilms were quantified by the percent transmittance (%Tbloc) method. Crystal Violet (CV) staining was used as marker of biofilm thickness, and XTT assay was used as a marker of the metabolic activity of Candida cells. The ability of biofilm formation was 99.2% in the non-invasive isolates versus 96.2% in the bloodstream isolates (%Tbloc vs.%Tbloc not significant). However, high biofilm production (%Tbloc, ≥35) was more frequent among the non-invasive isolates compared to the bloodstream isolates (78.1 vs. 72.5, p<0.001).
Efficacy of Debridement in Hematogenous and Early Post-Surgical Prosthetic Joint Infections
Authors: Vilchez Félix , Martínez-Pastor Juan C. , García-Ramiro Sebastián , Bori Guillem , Tornero Eduard , García Esther , Mensa Josep , Soriano Alex
Published: November 2011

Purposes

To review patients with a hematogenous and early post-surgical prosthetic joint infection (PJI) due to S. aureus treated with debridement and retention of the implant and to compare their clinical characteristics and outcome.

Methods

From January 2000 all patients with a prosthetic joint infection treated in a single-center were prospectively registered and followed-up. All potentially variables associated with outcome were recorded. For the present study, cases with a hematogenous or early post-surgical PJI due to S. aureus treated with debridement and at least 2 years of follow-up were reviewed. Cox regression model to identify factors associated with outcome were applied.

Results

12 hematogenous and 53 early post-surgical PJI due to S. aureus were included. Number of patients presenting with fever, leucocyte count, C-reactive protein concentration, and the number of bacteremic patients were significantly higher in hematogenous infections while the number of polymicrobial infections was lower in hematogenous than in early post-surgical infections. The global failure rate in hematogenous and early post-surgical PJI was 58.7% and 24.5%, respectively (p=0.02). The Cox regression model identified hematogenous infections (OR: 2.57, CI95%: 1.02–6.51, p=0.04) and the need of a second debridement (OR: 4.61, CI95%: 1.86–11.4, p=0.001) as independent predictors of failure.

Conclusion

Hematogenous infections were monomicrobial and had more severe symptoms and signs of infection than early post-surgical PJI. Hematogenous PJI due to S. aureus, using debridement with implant retention, had a worse outcome than early post-surgical infections.
Toll-Like Receptors (TLRs) in Innate Immune Defense Against Staphylococcus Aureus
Authors: Pietrocola Giampiero , Arciola Carla Renata , Rindi Simonetta , Di Poto Antonella , Missineo Antonino , Montanaro Lucio , Speziale Pietro
Published: November 2011

Toll-like receptors (TLRs) are the most important class of innate pattern recognition receptors (PRRs) by which host immune and non-immune cells are able to recognize pathogen-associated molecular patterns (PAMPs). Most mammalian species have 10 to 15 types of TLRs. TLRs are believed to function as homo- or hetero-dimers. TLR2, which plays a crucial role in recognizing PAMPs from Staphylococcus aureus, forms heterodimers with TLR1 or TLR6 and each dimer has a different ligand specificity. Staphylococcal lipoproteins, Panton-Valentine toxin and Phenol Soluble Modulins have been identified as potent TLR2 ligands. Conversely, the ligand function attributed to peptidoglycan and LTA remains controversial. TLR2 uses a MyD88-dependent signaling pathway that results in NF-κB translocation into the nucleus and activation of the expression of pro-inflammatory cytokine genes. Recognition rouses both an inflammatory response, culminating in the phagocytosis of bacteria, and an adaptive immune response, with the presentation of resulting bacterial compounds to T cells. Here, recent advances on the recognition of S. aureus by TLRs are presented and discussed, as well as the new therapeutic opportunities deriving from this new knowledge.
Influence of Co-Cr Particles and Co-Cr Ions on the Growth of Staphylococcal Biofilms
Authors: Hosman Anton H. , van der Mei Henny C. , Bulstra Sjoerd K. , Kuijer Roel , Busscher Henk J. , Neut Daniëlle
Published: November 2011

Purpose

In the last decades, hip prostheses with a metal-on-metal (MOM) bearing have been implanted by orthopedic surgeons worldwide. However, concerns are now raised towards the metal particles and degradation products released by MOM-bearings into surrounding tissue, although effects of Co-Cr wear on infection are also unknown. Therefore, we here determine the viable volumes of staphylococcal biofilms formed on polystyrene in the absence and presence of Co-Cr particles and Co-Cr ions.

Methods

Three clinically derived and two commercially available staphylococcal strains were grown in the presence of 2 mg/mL Co-Cr particles or 1000/500 μg/L Co-Cr ions derived from Co-Cr salts or from particle supernatant, under static and dynamic growth conditions. A dynamic model simulates the conditions that apply for biofilm formation in the human body, as synovial fluid in mobile patients with hip prostheses is in constant motion with accompanying shear rates. Images of 24 h old biofilms were made with confocal laser scanning microscopy and analyzed with the mathematical computer program COMSTAT, yielding the biovolume of a biofilm. X-ray photoelectron spectroscopy was performed on the particles to study their elemental surface composition.

Results

Most isolates showed a tendency of reduced biofilm growth in the presence of Co-Cr particles compared to growth during exposure to metal ions, but this was only significant in one strain under the dynamic growth condition (Staphylococcus aureus 7388). Characterization of the outer surface of the particles revealed a Co-Cr oxide layer enriched by Mo relative to the bulk concentration.

Conclusions

MOM bearings produce metal particles which were found to possess antibacterial characteristics under dynamic growth conditions. Further research is needed towards the clinical relevance of this finding.
Challenges in Periprosthetic Knee-Joint Infection
Authors: Sendi Parham , Zimmerli Werner
Published: November 2011

The number of knee arthroplasty procedures is growing and projected to further increase. The risk for periprosthetic joint infection (PJI) is estimated to be low (<1%). However, considering the increasing number of total knee arthroplasty, the increasing number of patients with multiple comorbidities, and the lifelong risk for acquiring hematogenous infection, the total number of PJI will further increase. Despite existing treatment concepts for PJI of the knee, there are still questions to solve, such as type of debridement surgery in case of implant retention, the role of a spacer from a microbiological perspective, and the optimal duration of antimicrobial therapy. In this review, these questions will be analyzed according to the available literature and the experience of the authors. Moreover, we review the most recent data on infection, risk factors, and microbiology of PJI.
Concise Survey of Staphylococcus Aureus Virulence Factors that Promote Adhesion and Damage to Peri-Implant Tissues
Authors: Arciola Carla Renata , Visai Livia , Testoni Francesca , Arciola Susanna , Campoccia Davide , Speziale Pietro , Montanaro Lucio
Published: November 2011

Staphylococcus aureus is the leading cause of infection in orthopedic implants and of osteomyelitis consequent to it. Here we focus on the wide array of virulence factors that endow S. aureus with its abilities to colonize peri-prosthesis tissues and to attack and damage them. Following an infective strategy orchestrated by agr locus, Staphylococcus aureus first deploys virulence factors for adhesion to the prosthesis and peri-prosthesis tissues and then launches its attack by delivering destructive factors.
Poly(Ethylene Glycol) and Hydroxy Functionalized Alkane Phosphate Self-Assembled Monolayers Reduce Bacterial Adhesion and Support Osteoblast Proliferation
Authors: Bozzini Sabrina , Petrini Paola , Tanzi Maria Cristina , Arciola Carla Renata , Tosatti Samuele , Visai Livia
Published: November 2011

Purpose

Presently there is interest today in designing improved titanium surfaces capable of high bioactivity in order to promote strong anchorage of the bone surrounding implants while at the same time discouraging bioadhesion. Poly(ethylene glycol)-modified (PEG) alkane phosphate and OH-terminated alkane phosphates have been demonstrated to be spontaneously adsorbed onto titanium oxide surfaces and produce surfaces with different protein resistance in relation to the PEG surface density. This study aims to evaluate caries-associated Streptococcus mutans (S. mutans) adhesion and osteoblast proliferation while varying the PEG surface density of titanium surfaces.

Methods

Bacterial adhesion was quantified by fluorescence microscopy and SAOS-2 human osteoblast proliferation was evaluated up to 7 days of culture in vitro. Metabolic activity of osteoblasts was measured by MTT test and the secretion of extracellular matrix proteins (osteopontin, osteocalcin and type I collagen) in culture medium was determined by immunoenzymatic assays.

Results

As the PEG surface density increased, the bacterial adhesion considerably decreased when compared to uncoated titanium surfaces. The monomolecular coatings proved to be capable of supporting osteoblast proliferation with the greatest levels of metabolic activity at the highest PEG surface concentrations.

Conclusions

These results are extremely promising for potential clinical application in implant uses where both reduction of bacteria adhesion and stimulation of bone formation are highly desirable.
Exopolysaccharide Production by Staphylococcus Epidermidis and its Relationship with Biofilm Extracellular DNA
Authors: Campoccia Davide , Montanaro Lucio , Ravaioli Stefano , Pirini Valter , Cangini Ilaria , Arciola Carla Renata
Published: November 2011

Implant-related infections are difficult to treat because they are very often associated with biofilm-forming micro-organisms capable of resisting host immune defenses and surviving conventional antibiotic treatments. In Staphylococcus epidermidis biofilm-forming strains, the polysaccharide intercellular adhesin (PIA), whose expression is encoded by the icaADBC operon, is recognized as a main staphylococcal accumulation mechanism. Nevertheless, various observations have shown that PIA expression is dispensable and a variety of additional/alternative accumulation mechanisms, including extracellular DNA (eDNA) and several other factors of proteic nature, can compensate for icaADBC low expression or even for its absence. A suggestive hypothesis points to the possibility that changes in biofilm extracellular matrix composition can be induced in different environmental niches. In this study we aimed at investigating the relationship between the exopolysaccharide and eDNA biofilm components, screening 55 S. epidermidis clinical isolates by means of a simple fluorescence-based microtiter-plate assay. Our findings indicate the existence of a certain degree of correlation, although not a strict one, between eDNA and the exopolysaccharide component. The presence of exopolysaccharide greatly varied even in strains belonging to the same strain type determined by automated riboprinting.
Extracellular DNA in Biofilms
Authors: Montanaro Lucio , Poggi Alessandro , Visai Livia , Ravaioli Stefano , Campoccia Davide , Speziale Pietro , Arciola Carla Renata
Published: November 2011

Extracellular DNA (eDNA) is an important biofilm component that was recently discovered. Its presence has been initially observed in biofilms of Pseudomonas aeruginosa, Streptococcus intermedius, Streptococcus mutans, then Enterococcus faecalis and staphylococci. Autolysis is the common mechanism by which eDNA is released. In P. aeruginosa eDNA is generated by lysis of a bacterial subpopulation, under control of quorum sensing system. In E. faecalis autolysis proceeds in a fratricide mode, resulting from a process similar to necrosis of eukaryotic cells. In Staphylococcus aureus autolysis originates by an altruistic suicide, i.e., a programmed cell death similar to apoptosis of eukaryotic cells. In S. aureus autolysis is mediated by murein hydrolase, while in S. epidermidis by the autolysin protein AtlE. In P. aeruginosa eDNA is located primarily in the stalks of mushroom-shaped multicellular structures. In S. aureus the crucial role of eDNA in stabilizing biofilm is highlighted by the disgregating effect of DNase I. eDNA represents an important mechanism for horizontal gene transfer in bacteria. eDNA and other microbial structural motifs are recognized by the innate immune system via the TLR family of pattern recognition receptors (PRRs).
Emerging Pathogenetic Mechanisms of the Implant-Related Osteomyelitis by Staphylococcus Aureus
Authors: Montanaro Lucio , Testoni Francesca , Poggi Alessandro , Visai Livia , Speziale Pietro , Arciola Carla Renata
Published: November 2011

Implant-related osteomyelitis is a severe and deep infection of bone that arises and develops all around an implant. Staphylococcus aureus is the first cause of osteomyelitis, whether implant-related or not. Bone is an optimal substratum for S. aureus, since this bacterium expresses various adhesins by which can adhere to bone proteins and to the biomaterial surfaces coated with the proteins of the host extracellular matrix. S. aureus is able not only to colonize bone tissues, but also to invade and disrupt them by entering bone cells and inducing cell death and osteolysis. Here we illustrate the pathogenetic mechanisms that can explain how the osteomyelitis sets in and develops around an implant.
Antibacterial Effects of Six Endodontic Sealers
Authors: Poggio Claudio , Lombardini Marco , Colombo Marco , Dagna Alberto , Saino Enrica , Arciola Carla Renata , Visai Livia
Published: November 2011

Purpose

The objective of this study was to perform an in vitro evaluation of the antibacterial properties of 6 endodontic sealers (Endomethasone C, Argoseal, Bioseal Normal, Acroseal, AH Plus, Sicura Seal).

Methods

The agar diffusion test (well and paper disc methods) with Enterococcus faecalis, Staphylococcus aureus and Streptococcus mutans was used. For the well method, Petri dishes were inoculated with bacterial suspensions. Each well was completely filled with freshly mixed endodontic sealer. For the paper disc method, sterile paper discs were immersed in freshly mixed sealers and put on agar plates. Diameters of halos formed around the sealers were measured after 24 h and 48 h. Statistical analysis: The effects of well method and of paper disc method were analyzed by 1-way ANOVA.

Results

Endomethasone C, Argoseal and Bioseal showed the largest inhibition halos for all the tested microorganisms, while Sicura Seal and AH Plus showed low antibacterial effects. Moreover, the comparison of well method and paper disc methods showed significant statistical differences (P<0,01) for all sealers and indicated a dose-dependent antimicrobial effect.
Photoactivated Disinfection (PAD) in Endodontics: an in vitro Microbiological Evaluation
Authors: Poggio Claudio , Arciola Carla Renata , Dagna Alberto , Florindi Filippo , Chiesa Marco , Saino Enrica , Imbriani Marcello , Visai Livia
Published: November 2011

Purpose

The objective of the present study was the in vitro evaluation by MTT test of the antimicrobial effect of photoactivated disinfection (PAD) and, comparatively, of a conventional 5.25% NaOCl irrigating solution.

Methods

Enterococcus faecalis, Streptococcus mutans and Streptococcus sanguis strains were selected for the test. Freshly extracted single-rooted human teeth were endodontically treated, inoculated with bacterial strains and then divided into different groups, each of them treated with PAD, with PAD plus 0.5% NaOCl solution, with TBO, with PAD for longer time and with 5% NaOCl solution (positive control).

Results

The results were significantly different among the various groups, and for Enterococcus faecalis, Streptococcus mutans and Streptococcus sanguis. PAD applied for a longer time (in respect to manufacturer's instructions) or PAD associated to 5% NaOCl showed the significantly higher antibacterial effects.
Biofilm Extracellular-DNA in 55 Staphylococcus Epidermidis Clinical Isolates from Implant Infections
Authors: Ravaioli Stefano , Campoccia Davide , Visai Livia , Pirini Valter , Cangini Ilaria , Corazzari Tolmino , Maso Alessandra , Poggio Claudio , Pegreffi Francesco , Montanaro Lucio , Arciola Carla Renata
Published: November 2011

Biofilm formation is broadly recognized as an important virulence factor in many bacterial species implicated in implant-related opportunistic infections. In spite of a long history of research and many investigative efforts aimed at elucidating their chemical composition, structure, and function, the nature of bacterial biofilms still remains only partly revealed. Over the years, different extracellular polymeric substances (EPS) have been described that contribute functionally and structurally to the organization of biofilms. Recently extracellular DNA (eDNA) has emerged as a quantitatively conspicuous and potentially relevant structural component of microbial biofilms of many microbial species, Staphylococcus aureus and S. epidermidis among them. The present study aims at comparatively investigating the amount of eDNA present in the biofilm of 55 clinical isolates of S. epidermidis from postsurgical and biomaterial-related orthopedic infections. Quantification of eDNA was performed by a non-destructive method directly on bacterial biofilms formed under static conditions on the plastic surface of 96-well plates.
Internalization by Osteoblasts of Two Staphylococcus Aureus Clinical Isolates Differing in their Adhesin Gene Pattern
Authors: Testoni Francesca , Montanaro Lucio , Poggi Alessandro , Visai Livia , Campoccia Davide , Arciola Carla Renata
Published: November 2011

Staphylococcus aureus is the leading etiologic agent of implant orthopedic infections. Until recently S. aureus was considered a mere extracellular pathogen; it then turned out to be able to invade eukaryotic cells. Adhesion of S. aureus to peri-prosthesis tissues represents the starting of the infection pathogenesis and the first step of the subsequent internalization of S. aureus by host cells. In the present work the experimental observations on two epidemic clinical strains differing in their adhesin pattern demonstrate the crucial role of the fibronectin-binding protein A in the internalization process and suggest that CNA and Bbp adhesins can play a synergistic role by acting in the initial adhesion of S. aureus to osteoblasts, thus favoring the subsequent FnBPA-mediated internalization.
Bone Reconstruction: Au Nanocomposite Bioglasses with Antibacterial Properties
Authors: Grandi Stefania , Cassinelli Valentina , Bini Marcella , Saino Enrica , Mustarelli Piercarlo , Arciola Carla Renata , Imbriani Marcello , Visai Livia
Published: November 2011

Bioglasses are of wide interest since they spontaneously bond and integrate with living bone in the body. By varying the glass chemistry and/or by adding some dopants, it is possible to improve their clinical applications. Gold nanoparticles (Au NPs) are a well-known antibacterial agent, as well as a unique probe for sensing and imaging applications. We report on the synthesis of a 58S bioglass doped with Au NPs at two doping levels: 0.1% wt. and 1% wt. Antibacterial properties were observed on the Gram-positive Staphylococcus aureus, whereas no significant effects were found on the Gram-negative Escherichia coli. A possible mechanism of action of Au NPs towards bacteria has been described.
Bacterial DNA from Orthopedic Implants after Routine Removal
Authors: Obst Ursula , Marten Silke-Mareike , Niessner Christoph , Hartwig Erich
Published: November 2011

Bacterial 16S rDNA was monitored and identified from orthopedic metallic implants after routine or septic removal from patients in a German hospital. From March to June 2009, 28 metallic implants, 10 human biopsies, and 6 foam dressings from 28 patients were investigated. After analysis of this first collective, the methods were optimized to enhance sensitivity and to reduce interference with human DNA. Then a second collective consisting of 21 metallic implants from 21 patients was investigated from June 2009 to January 2010. In the first collective, 71% of the metallic implants were negative for eubacterial DNA. Pathogens such as Staphylococcus aureus and opportunists such as Lactobacillus rhamnosus were identified in 11% of the samples, whereas the residual 18% positive results were classified as from skin sources or could not be confirmed. Tissue, secretion, and bone samples as well as foam dressings from the same collective also contained pathogens and opportunists. After the optimization of the methods, a considerable increase of positive samples was seen: in the second collective 19 of the 21 metallic implants proved to be positive for eubacterial 16S rDNA. Bacterial DNA from environmental sources was detected in 13 samples, and in 20 specimens, predominantly mostly the skin. Opportunistic pathogens were detected in 19 samples. Interestingly, septic complications did not occur despite the presence of bacterial DNA. The results obtained up to now encourage us not only to continue a directed monitoring of bacterial DNA on orthopedic implants in practice but also to look intensely for possible sources of bacterial contamination during and after insertion or during removal of such implants.
Biofilm Growth on Implants: Bacteria Prefer Plasma Coats
Authors: Wagner Christof , Aytac Sara , Hänsch G. Maria
Published: November 2011

Purpose

Bacterial biofilm formation on prostheses or devices used for osteosynthesis is increasingly recognized as cause of persistent infections, an entity known as implant-associated posttraumatic osteomyelitis. Biofilm formation is a very complex, multistep process with adhesion as the first and decisive step. The most prevalent pathogens found are staphylococci species, especially S. aureus, presumably due to a preference to non-biological materials, such as metal. Adherence is influenced by several factors, including the microenvironment, in which blood proteins from serum or plasma might influence adhesion and maybe biofilm formation. The aim of the present study was to test and to compare adherence of S. aureus and P. aeruginosa to different biological and non-biological surfaces in vitro. The question was addressed if coating of the surface by plasma or serum proteins influences bacterial adherence.

Methods

Adherence of radiolabeled bacteria to different surfaces in the presence or absence or serum/plasma proteins was measured over time.

Results

When testing adherence of S. aureus to plastic, titanium or to monolayers of epithelial cells (A549) or fibroblasts (Colo800) a clear-cut preference for non-biological surfaces, especially for titanium was seen. Using P. aeruginosa species a similar pattern without a significant difference was revealed. When mimicking the in vivo situation by pre-coating of titanium with human serum or plasma adherence was increased, especially when titanium was coated (“opsonized”) by plasma.

Conclusions

Bacterial adherence to surfaces is determined by a variety of factors such as temperature, the presence of nutrients, the absence of host defense systems and the configuration of the covered surface. In vivo, adherence to non-biological surfaces is also influenced by the microenvironment, especially plasma proteins, promoting biofilm formation.
The Origins of Political Order and the Anglo-Saxon State
Authors: Brookes Stuart , Reynolds Andrew
Published: November 2011

How do ordered political societies come about – and what can archaeology offer to the debate? New research by a team at the UCL Institute of Archaeology is investigating the origins of English governance by exploring the impact on landscape of legal structures, law and order, and places of political assembly. Far from being shadowy and elusive, we argue that there is much that land-scape archaeology can provide to understand the ways in which pre-modern societies were governed.
Editorial Envitado
Authors: Picado Apolinar , Moncada Virginia
Published: November 2011

DOI: http://dx.doi.org/10.5377/nexo.v24i1.588 Nexo, Vol. 24, No. 1, pp. 2, 2011
Análisis numérico de la convección natural en recintos cerrados con distinto factor de forma
Authors: Lizardi A , Hernández A , Terrés H , López R , Morales JR , Lara A
Published: November 2011

En este trabajo se utilizó el análisis numérico, aplicando el programa de simulación para ingeniería ANSYS, para establecer la distribución de temperaturas, densidad y velocidades vertical y horizontal en una cavidad cerrada con relación geométrica alto/ancho (H/E) del sistema de 0.5, 1 y 2, temperatura constante en la pared vertical izquierda y derecha de 50 y 20 °C, respectivamente, y condición de frontera adiabática en las paredes horizontales. Lo anterior para un número de Prandtl de 4.83 y Rayleigh de 5.84x107. Al comparar los resultados entre el sistema con H/E = 2 y H/E = 1, se encontró que el valor máximo positivo de la velocidad vertical se incrementó un 26.29 %, el de la velocidad horizontal disminuyó 72.75 % y la temperatura en la zona central de la cavidad disminuyó un 2.46 %. Por otro lado, al comparar los resultados del sistema H/E = 0.5 y H/E = 1, se encontró que el valor máximo positivo de la velocidad vertical aumentó un 7.24 %, el de la velocidad horizontal se incrementó 34.08 % y la temperatura de la zona central del sistema disminuyó un 3.70 %. Palabras claves: Convección natural; Cavidad cerrada; ANSYS DOI: http://dx.doi.org/10.5377/nexo.v24i1.589   Nexo, Vol. 24, No. 1, pp. 3-10, 2011
Nuevas aportaciones a la gestión informatizada de derrames de hidrocarburos: su aplicación a "zonas refugio"
Authors: Bergueiro JR , Moreno S , Hernández L , Cavilla JM , Gómez JJ , González J
Published: November 2011

El objeto del presente trabajo es el de describir la mayor parte de los procedimientos a seguir para decidir si es aconsejable trasladar un petrolero siniestrado a una “zona refugio”. Para tomar esta decisión se deberán considerar diferentes procedimientos, con la finalidad de objetivizar al máximo dicha decisión. Es de gran importancia conocer muy bien las características y las infraestructuras de las diferentes zonas costeras que pueden ser consideradas posibles “zonas refugio”. En base a todo lo anterior, se ha desarrollado un programa formado por varios módulos que permiten obtener datos de gran importancia, entre los que se incluyen las matrices de valores ambientales e infraestructurales, y que permite el cálculo de determinados factores determinantes para las actuaciones de traslado y preparación del petrolero (tiempo de traslado del petrolero, tiempo de atraque y conexión a los sistemas de bombeo, tiempo de vaciado de los hidrocarburos a los depósitos de almacenamiento, trasvase a otro petrolero, etc.). Además, dicho programa permite estimar los costes de limpieza y restauración, así como las pérdidas en el sector turístico. Palabras claves: Hidrocarburos; Zona refugio; Derrames de hidrocarburos DOI: http://dx.doi.org/10.5377/nexo.v24i1.590   Nexo, Vol. 24, No. 1, pp. 11-19, 2011
Estudio de la cinética de adsorción de Cu y Hg a partir de soluciones binarias usando quitosano
Authors: Matus I , Paniagua L , Benavente M
Published: November 2011

En este trabajo se estudió la cinética de adsorción de Cu(II) y Hg(II) en quitosano a partir de una solución binaria, a diferentes concentraciones iniciales de los iones metálicos, tamaño de partículas del adsorbente y velocidad de agitación. El quitosano fue extraído por métodos químicos de caparazón de camarón. Soluciones de 1 L de Cu(II) y Hg(II) fueron puestas en contacto con 2 g de quitosano y se agitaron por un período de 8 h. Al final del proceso, las muestras fueron analizadas en un espectrómetro de absorción atómica. Los datos experimentales fueron evaluados aplicando los modelos cinéticos de pseudo-primer orden y pseudo-segundo orden. Los resultados del proceso de adsorción de los iones metálicos Cu(II) y Hg(II) con quitosano, mostraron que en la mayoría de los casos, ambos iones fueron eficazmente adsorbidos por la quitosano, obteniéndose un porcentaje de adsorción entre 44-100 % para Cu(II) y entre 95-100 % para el Hg(II). Para ambos iones, los resultados mostraron que a bajas concentraciones el proceso de adsorción se ajusta mejor al modelo de pseudo-primer orden y a concentraciones altas el modelo que mejor se ajusta a los datos experimentales es el modelo de pseudo-segundo orden; es decir, el paso limitante en la velocidad es la reacción de adsorción y no la transferencia de masa. Palabras claves: Caparazón de camarón; Cinética de adsorción; Modelos cinéticos; Solución binaria; Quitosano DOI: http://dx.doi.org/10.5377/nexo.v24i1.591   Nexo, Vol. 24, No. 1, pp. 20-32, 2011
Estudio de la fermentación láctica para la extracción de quitina a partir de desechos de crustáceos
Authors: Marcia E , Malespín J , Sánchez M , Benavente M
Published: November 2011

La extracción de quitina a partir de desechos de crustáceos involucró la fermentación acido láctica para la desproteinización y desmineralización del caparazón de camarón, haciendo uso de suero de leche y sacarosa, como sustrato y fuente de carbono. El proceso de fermentación se llevo a cabo en un reactor vertical de vidrio Pyrex de 4 L por un período de 2 y 3 semanas a temperatura ambiente. Los resultados mostraron que aunque hubo una buena desproteinización y desmineralización, todavía el producto contenía restos de proteínas y pigmentos. Por ello, se hizo necesario aplicar un procedimiento químico con hidróxido de sodio e hipoclorito de sodio, para remover completamente las proteínas y los pigmentos de la estructura del caparazón. Al final del proceso se obtuvo una recuperación del 85 %. La comparación de los espectros FT-IR de la quitina producida con una muestra de quitina comercial, mostró un porcentaje de correlación del 93-95 %, lo que indica que la quitina obtenida utilizando el método combinado, tiene un alto grado de pureza. Palabras claves: Caparazón de camarón; Quitina; Reactor vertical; Sacarosa; Suero de leche   DOI: http://dx.doi.org/10.5377/nexo.v24i1.592   Nexo, Vol. 24, No. 1, pp. 33-42, 2011
Salar de Surire un ecosistema altoandino en peligro, frente a escenario del cambio climático
Authors: Garcés I
Published: November 2011

Este trabajo realiza un análisis al salar de Surire desde el punto de vista de la biodiversidad y sus implicancias producto del cambio climático. Como resultado se predice que los próximos años serán secos y la temperatura podría ir en aumento, lo cual afectará notablemente a la flora y fauna del altiplano. El salar de Surire es un cuerpo salino ubicado en el altiplano andino chileno, en un entorno geológico de características volcánicas. La climatología actual de aridez no permite una acumulación de agua superficial de gran extensión, y por lo tanto es posible diferenciar tres tipos principales de aguas: los aportes de drenaje, las acumulaciones de agua en la aureola pantanosa externa o “bofedales”, y las aguas del interior del cuerpo salino (surgencias termales y salmueras). Estas condiciones hidrológicas afectan factores abióticos, como anaerobiosis de suelos, disposición de nutrientes y salinidad, factores determinantes del desarrollo de la flora y fauna. Palabras claves: Salar de Surire; Biodiversidad andina; Cambio climático; Ecosistema andino DOI: http://dx.doi.org/10.5377/nexo.v24i1.593   Nexo, Vol. 24, No. 1, pp. 43-49, 2011
Simulación y experimentación de laminación plana de placas de aluminio 6063
Authors: Robert T , Vázquez O , López E
Published: November 2011

Se generó una metodología experimental para el entendimiento teórico-práctico de los conceptos del proceso de laminación plana en frío. Se laminaron placas de aluminio de aproximadamente 100 mm de longitud y 9 mm de espesor, a diferentes anchos: 10 y 30 mm. Se seleccionó una razón de reducción constante de 0.3 mm para cada paso de laminación, hasta lograr una reducción superior al 80 % en espesor. Se implementó un modelo matemático en el paquete comercial Abaqus® con el fin de obtener un mayor entendimiento sobre la influencia de las variables del proceso (fuerza aplicada y dimensiones de las probetas) en los campos de esfuerzos y deformaciones que, experimentalmente, no se pueden observar. Se encontró, mediante la simulación matemática, que se produce un endurecimiento superficial en las placas y que la deformación obtenida es heterogénea, lo cual se corrobora físicamente. Palabras claves: Laminación plana; Aluminio 6063-Al; Sistema de adquisición de datos; Simulación DOI: http://dx.doi.org/10.5377/nexo.v24i1.594   Nexo, Vol. 24, No. 1, pp. 50-60, 2011
Caracterización reológica de soluciones azucaradas para el proceso de evaporación-cristalización
Authors: Gómez A Martinez , Bazán I Sánchez , Osorio-Mirón A , Zamora L López , Sánchez Bazán LA , Aguilar E Hernández Aguilar
Published: November 2011

En este trabajo se realizó un estudio experimental para la caracterización reológica de soluciones azucaradas en el proceso de producción de azúcar. El objetivo principal fué la caracterización de soluciones azucaradas con el fin de modelar su comportamiento reológico para la optimización del proceso de evaporación-cristalización en una etapa posterior. En los experimentos, se utilizó un diseño de experimento tipo factorial 3k, en donde se considera la interacción de tres factores en la determinación de la variable de respuesta; en este caso los factores son: la concentración (ºBx), la temperatura y las revoluciones por minuto (velocidad de corte), cada uno con tres niveles, tomando como variable de respuesta la viscosidad. El desarrollo experimental y el análisis de resultados conduce a la determinación del modelo reológico de las soluciones problema en el rango de estudio de los factores de interés, proponiéndose un modelo tipo Ostwald-de Waele para fluidos dilatantes. Palabras claves: Modelo reológico; Velocidad de corte; Viscosidad DOI: http://dx.doi.org/10.5377/nexo.v24i1.595 Nexo, Vol. 24, No. 1, pp. 61-71, 2011
Berberine Improves Glucose Homeostasis in Streptozotocin-Induced Diabetic Rats in Association with Multiple Factors of Insulin Resistance
Authors: Chen Yanfeng , Wang Yanwen , Zhang Junzeng , Sun Changhao , Lopez Alfonso
Published: November 2011

The present study was carried out to determine the effect of berberine on glucose homeostasis and several biomarkers associated with insulin sensitivity in male Wistar rats with intraperitoneal injection of streptozotocin (STZ)-induced diabetes. Rats with fasting blood glucose 16.7 mmol/L after 2 weeks of STZ injection were divided into two groups. One group was used as the diabetic control and another treated by gavage feeding with 100 mg/kg/d of berberine in water containing 0.5% carboxymethyl cellulose. A group of rats without receiving STZ was used as the normal control. After 7 weeks, berberine supplementation moderately but significantly lowered fasting blood glucose levels and improved oral glucose tolerance. Berberine lowered plasma free fatty acids and C-reactive protein levels without affecting plasma insulin levels. Diabetic rats treated with berberine showed significantly lower plasma triacylglycerol and cholesterol levels. Furthermore, berberine inhibited dipeptidyl peptidase-4 and protein tyrosine phosphatase-1B activities. In conclusion, berberine showed a dramatic effect of lowering blood cholesterol and triacylglycerols and improved moderately glucose homeostasis in STZ-induced diabetic rats in association with multiple factors related to insulin resistance.
A Conceptual Model Facilitating the Transition of Involuntary Migrant Families
Authors: Samarasinghe Kerstin Linnéa
Published: November 2011

Refugee families face a complex transition due to the nature of involuntary migration and the process of acculturation. There are several risk factors to the family adaptation process during the transition period, which are sociocontextually environmental dependant. Facilitating a healthy transition for refugee families, therefore, requires the role of nursing to incorporate sociopolitics into the discipline. This paper introduces a sociopolitically oriented and community-driven assessment and intervention model which is based on a family systematic approach. Interventions that aid the families in their acculturation process as well as empowers them to a well-functioning daily life, as per the SARFI model, should be adopted. As such, the future of nursing may provide additional primary health care services for refugee families; this is through a team-led “family nurse” who provides quality care for the family unit in collaboration with other health care professionals and societal authorities.
Cubic Spline Method for 1D Wave Equation in Polar Coordinates
Authors: Mohanty R. K. , Kumar Rajive , Dahiya Vijay
Published: November 2011

Using nonpolynomial cubic spline approximation in space and finite difference in time direction, we discuss three-level implicit difference scheme of O(k2+h4) for the numerical solution of 1D wave equations in polar coordinates, where k>0 and h>0 are grid sizes in time and space coordinates, respectively. The proposed method is applicable to problems with singularity. Stability theory of the proposed method is discussed, and numerical examples are given in support of the theoretical results.
The red queen and her king: Cooperation at all levels of life
Authors: Weiss Kenneth M. , Buchanan Anne V. , Lambert Brian W.
Published: November 2011

The Red Queen in “Through the Looking Glass” is often used as a metaphor for the relentless, unremitting competitive struggle by which Darwin described life. That imagery fits comfortably in our culture, with its emphasis on competition and inequity, but less so for nature herself. Life is manifestly much more about cooperation, at all levels and through a variety of ubiquitous mechanisms, than it is about competition. Most organisms of most species are nowhere near the proverbial Malthusian edge of survival, such that selection will detect the tiniest difference in their performance and enhance its genetic basis. Cooperation through interaction of multiple entities is inherent in many fundamental aspects of life, and its importance is not widely enough appreciated. Here we discuss a set of principles by which this works. We illustrate the points with a computer simulation of a topic of interest to anthropology, the development of the head. In a sense, our culture has its metaphors reversed. The red royal family is a more accurate symbol for the true nature of life, human or otherwise. Yrbk Phys Anthropol 54:3–18, 2011. © 2011 Wiley Periodicals, Inc.
GIS and paleoanthropology: Incorporating new approaches from the geospatial sciences in the analysis of primate and human evolution
Authors: Anemone R.L. , Conroy G.C. , Emerson C.W.
Published: November 2011

The incorporation of research tools and analytical approaches from the geospatial sciences is a welcome trend for the study of primate and human evolution. The use of remote sensing (RS) imagery and geographic information systems (GIS) allows vertebrate paleontologists, paleoanthropologists, and functional morphologists to study fossil localities, landscapes, and individual specimens in new and innovative ways that recognize and analyze the spatial nature of much paleoanthropological data. Whether one is interested in locating and mapping fossiliferous rock units in the field, creating a searchable and georeferenced database to catalog fossil localities and specimens, or studying the functional morphology of fossil teeth, bones, or artifacts, the new geospatial sciences provide an essential element in modern paleoanthropological inquiry. In this article we review recent successful applications of RS and GIS within paleoanthropology and related fields and argue for the importance of these methods for the study of human evolution in the twenty first century. We argue that the time has come for inclusion of geospatial specialists in all interdisciplinary field research in paleoanthropology, and suggest some promising areas of development and application of the methods of geospatial science to the science of human evolution. Yrbk Phys Anthropol 54:19–46, 2011. © 2011 Wiley Periodicals, Inc.
The roles of the immune system in Women's reproduction: Evolutionary constraints and life history trade‐offs
Authors: Abrams Elizabeth T. , Miller Elizabeth M.
Published: November 2011

Life history theory posits that, as long as survival is assured, finite resources are available for reproduction, maintenance, and growth/storage. To maximize lifetime reproductive success, resources are subject to trade‐offs both within individuals and between current and future investment. For women, reproducing is costly and time‐consuming; the bulk of available resources must be allocated to reproduction at the expense of more flexible systems like immune function. When reproducing women contract infectious diseases, the resources required for immune activation can fundamentally shift the patterns of resource allocation. Adding to the complexity of the reproductive‐immune trade‐offs in women are the pleiotropic effects of many immune factors, which were modified to serve key roles in mammalian reproduction. In this review, we explore the complex intersections between immune function and female reproduction to situate proximate immunological processes within a life history framework. After a brief overview of the immune system, we discuss some important physiological roles of immune factors in women's reproduction and the conflicts that may arise when these factors must play dual roles. We then discuss the influence of reproductive‐immune trade‐offs on the patterning of lifetime reproductive success: (1) the effect of immune activation/infectious disease on the timing of life history events; (2) the role of the immune system, immune activation, and infectious disease on resource allocation within individual reproductive events, particularly pregnancy; and (3) the role of the immune system in shaping the offspring's patterns of future life history trade‐offs. We close with a discussion of future directions in reproductive immunology for anthropologists. Yrbk Phys Anthropol 54:134–154, 2011. © 2011 Wiley Periodicals, Inc.
Brief communication: Enamel thickness and durophagy in mangabeys revisited
Authors: McGraw W. Scott , Pampush James D. , Daegling David J.
Published: November 2011

The documentation of enamel thickness variation across primates is important because enamel thickness has both taxonomic and functional relevance. The Old World monkeys commonly referred to as mangabeys have figured prominently in investigations of feeding ecology and enamel thickness. In this article, we report enamel thickness values for four mangabey taxa (Cercocebus atys, Cercocebus torquatus, Lophocebus aterrimus, and Lophocebus albigena), offer revised interpretation of the significance of thick enamel in papionin evolution, and place our new data in a broader comparative framework. Our data indicate that all mangabeys have thick enamel and that the values obtained for Cercocebus and Lophocebus equal or exceed those published for most extant non‐human primates. In addition, new field data combined with a current reading of the dietary literature indicate that hard foods make up a portion of the diet of every mangabey species sampled to date. Clarification on the relationship between diet and enamel thickness among mangabeys is important not only because of recognition that mangabeys are not a natural group but also because of recent arguments that explain thick enamel as an evolved response to the seasonal consumption of hard foods. Am J Phys Anthropol 147:326–333, 2012. © 2011 Wiley Periodicals, Inc.