Transport of heat and mass in a two-phase mixture. From a continuous to a discontinuous description

We present a theory which describes the transport properties of the interfacial region with respect to heat and mass transfer. Postulating the local Gibbs relation for a continuous description inside the interfacial region, we derive the description of the Gibbs surface in terms of excess densities and fluxes along the surface. We introduce overall interfacial resistances and conductances as the coefficients in the force-flux relations for the Gibbs surface. We derive relations between the local resistivities for the continuous description inside the interfacial region and the overall resistances of the surface for transport between the two phases for a mixture. It is shown that interfacial resistances depend among other things on the enthalpy profile across the interface. Since this variation is substantial the coupling between heat and mass flow across the surface are also substantial. In particular, the surface puts up much more resistance to the heat and mass transfer then the homogeneous phases over a distance comparable to the thickness of the surface. This is the case not only for the pure heat conduction and diffusion but also for the cross effects like thermal diffusion. For the excess fluxes along the surface and the corresponding thermodynamic forces we derive expressions for excess conductances as integrals over the local conductivities along the surface. We also show that the curvature of the surface affects only the overall resistances for transport across the surface and not the excess conductivities along the surface.Comment: 25 pages, 2 figure

The role of fatty acid desaturases in epidermal metabolism

The lipid composition of skin is important to a variety of functions served by this organ. Therefore, skin expresses multiple enzymes that synthesize and metabolize lipids. An important class of lipid metabolism enzymes expressed in skin is the lipid desaturases. Various isoforms of stearoyl-CoA desaturase, a delta-9 desaturase, as well as a delta-6 desaturase alter the lipid composition of the skin, thereby affecting skin barrier homeostasis and consequently, whole body energy balance. This review will focus on the role of fatty acid desaturases in maintaining epidermal metabolism

Radiotherapy for Soft Tissue Sarcomas after Isolated Limb Perfusion and Surgical Resection: Essential for Local Control in All Patients?

Background: Standard treatment for localized soft tissue sarcoma (STS) is resection plus adjuvant radiotherapy (RTx). In approximately 10% of cases, resection would cause severe loss of function or even require amputation because of the extent of disease. Isolated limb perfusion (ILP) with tumor necrosis factor alpha (TNF-α) and melphalan can achieve regression of the tumor, facilitating limb-saving resection. RTx improves local control but may lead to increased morbidity. Methods: In our database of over 500 ILPs, 122 patients with unifocal STS were treated by ILP followed by limb-sparing surgery. All included patients were candidates for amputation. Results: Surgery resulted in 69 R0 resections (57%), and in 53 specimens (43%) resection margins contained microscopic evidence of tumor (R1). Histopathological examination revealed >50% ILP-induced tumor necrosis in 59 cases (48%). RTx was administered in 73 patients (60%). Local recurrence rate was 21% after median follow-up of 31 months (2-182 months). Recurrence was significantly less in patients with >50% ILP-induced necrosis versus ≤50% necrosis (7% vs. 33%, P = 0.001). A similar significant correlation was observed for R0 versus R1 resections (15% vs. 28%, P = 0.04). In 36 patients with R0 resection and >50% necrosis, of whom 21 were spared RTx, no recurrences were observed during follow-up. Conclusions: In patients with locally advanced primary STS, treated with ILP followed by R0 resection, and with >50% ILP-induced necrosis in the resected specimen, RTx is of no further benefit

Metabolism and functional effects of plant-derived omega-3 fatty acids in humans

Alpha-linolenic acid (ALA) is an essential fatty acid and the substrate for the synthesis of longer-chain, more un- saturated ω-3 fatty acids, eicosapentaenoic acid (EPA), docosapentaenoic acid and docosahexaenoic acid (DHA). EPA and DHA are associated with human health benefits. The primary source of EPA and DHA is seafood. There is a need for sustainable sources of biologically active ω-3 fatty acids. Certain plants contain high concentrations of ALA and stearidonic acid (SDA). Here we review the literature on the metabolism of ALA and SDA in humans, the impact of increased ALA and SDA consumption on concentrations of EPA and DHA in blood and cell lipid pools, and the extent to which ALA and SDA might have health benefits. Although it is generally considered that humans have limited capacity for conversion of ALA to EPA and DHA, sex differences in conversion to DHA have been identified. If conversion of ALA to EPA and DHA is limited, then ALA may have a smaller health benefit than EPA and DHA. SDA is more readily converted to EPA and appears to offer better potential for health improvement than ALA. However, conversion of both ALA and SDA to DHA is limited in most humans

Site-specific differences in fatty acid composition of dendritic cells and associated adipose tissue in Popliteal Depot, Mesentery, and Omentum and their modulation by chronic inflammation and dietary lipids

Background: This study explores the role of lymphatics-associated adipocytes in determining the lipid composition of dendritic cells. Methods and Results: Adult male rats were fed plain chow, or chow supplemented with 20% sunflower or fish oil. Chronic local inflammation was induced by subcutaneous injection of 20 µg lipopolysaccharide three times a week for 2 weeks near the popliteal lymph nodes. Chemokine-stimulated dendritic cells were collected over 4 h from popliteal and mesenteric lymph nodes, and perinodal and other samples of mesenteric, popliteal and omental adipose tissue. Fatty acids extracted from triacylglycerols and/or phospholipids were separated and quantified by gas chromatography from each sample of dendritic cells and intracellular lipids, membranes, stroma and isolated adipocytes from the adipose tissue. Dendritic cells from lymph nodes and adipose tissue samples differ in fatty acid composition, and can be modulated by diet. The site-specific differences of dendritic cells correlate with those of the contiguous adipocytes. Chronic mild stimulation alters the lipid composition of dendritic cells near the inflamed site and elsewhere; changes are minimal after the fish-oil diet. The composition of adipocyte triacylglycerol and phospholipid fatty acids also changes near the stimulation site in ways that counteract alterations induced by the experimental diets. Conclusions: Fatty acids in dendritic cells differ with anatomical site, and are determined by the adjacent adipocytes, which actively regulate their own lipid composition. These findings demonstrate functional bases for the anatomical associations between adipose and lymphoid tissues and may be a mechanism by which dietary lipids modulate the immune system

Concerning Selectivity in the Oxidation of Peptides by Dioxiranes. Further Insight into the Effect of Carbamate Protecting Groups

With use ofmethyl(trifluoromethyl)dioxirane (TFDO), the oxidation of some tripeptide esters protected at the N-terminus with carbamate or amide groups could be achieved efficiently under mild conditions with no loss of configuration at the chiral centers. Expanding on preliminary investigations, it is found that, while peptides protected with amide groups (PG=Ac-, Tfa-, Piv-) undergo exclusive hydroxylation at the side chain, their analogues bearing a carbamate group (PG=Cbz-, Moc-, Boc-, TcBoc-) give competitive and/or concurrent hydroxylation at the terminalN-Hmoiety. Valuable nitro derivatives are also formed as a result of oxidative deprotection of the carbamate group with excess dioxirane. A rationale is proposed to explain the dependence of the selectivity upon the nature of the protecting group