6,193 research outputs found
Modelling the kinetics of thermal inactivation of apple polyphenoloxidase
The enzymatic browning of fruits and vegetables caused by mechanical injury during postharvest storage or processing is initiated by the catalytic action of polyphenoloxidase (PPO). A bleaching
treatment prior to processing is still considered mostly effective in inhibiting the catalytic activity of PPO,
and thus controlling undesirable enzymatic browning. In this work, different mathematical routines were
assessed in terms of their adequacy to describe the thermal inactivation of PPO from Golden apples over a
range of temperatures from 62.5 to 72.5 ºC. The classical approach to kinetic modelling of the decay activity
of apple PPO, commonly reported to follow a first-order model, employs a two-step procedure, in which the
model parameters are individually obtained, by each temperature studied, using non-linear or linear
regressions. Thereafter, the estimated parameters are further used to calculate their temperature dependence.
Alternatively, a one-step method provides a regression fit to all experimental data sets, with the temperature
dependence equation being directly built in the kinetic model. This fitting technique thus, (a) avoids the
estimation of intermediate parameters and, (b) substantially increases the degrees of freedom and hence the
precision of parameters’ estimates. Within this issue was further explored the logarithmic transformation of
the mathematical equations used on the adequacy of the model to describe experimental data. In all cases
non-weighted least-squares regression procedures were used. Both the examination and criticism of the
current modelling strategies were done by assessing statistical data obtained, such as the confidence intervals
of the estimates, correlation coefficients, sum of squares, and residuals normality
Theory of one and two donors in Silicon
We provide here a roadmap for modeling silicon nano-devices with one or two
group V donors (D). We discuss systems containing one or two electrons, that
is, D^0, D^-, D_2^+ and D_2^0 centers. The impact of different levels of
approximation is discussed. The most accurate instances -- for which we provide
quantitative results -- are within multivalley effective mass including the
central cell correction and a configuration interaction account of the
electron-electron correlations. We also derive insightful, yet less accurate,
analytical approximations and discuss their validity and limitations -- in
particular, for a donor pair, we discuss the single orbital LCAO method, the
Huckel approximation and the Hubbard model. Finally we discuss the connection
between these results and recent experiments on few dopant devices.Comment: 13 pages, 6 figure
Impact of the valley degree of freedom on the control of donor electrons near a Si/SiO_2 interface
We analyze the valley composition of one electron bound to a shallow donor
close to a Si/barrier interface as a function of an applied electric field. A
full six-valley effective mass model Hamiltonian is adopted. For low fields,
the electron ground state is essentially confined at the donor. At high fields
the ground state is such that the electron is drawn to the interface, leaving
the donor practically ionized. Valley splitting at the interface occurs due to
the valley-orbit coupling, V_vo^I = |V_vo^I| e^{i theta}. At intermediate
electric fields, close to a characteristic shuttling field, the electron states
may constitute hybridized states with valley compositions different from the
donor and the interface ground states. The full spectrum of energy levels shows
crossings and anti-crossings as the field varies. The degree of level
repulsion, thus the width of the anti-crossing gap, depends on the relative
valley compositions, which vary with |V_vo^I|, theta and the interface-donor
distance. We focus on the valley configurations of the states involved in the
donor-interface tunneling process, given by the anti-crossing of the three
lowest eigenstates. A sequence of two anti-crossings takes place and the
complex phase theta affects the symmetries of the eigenstates and level
anti-crossing gaps. We discuss the implications of our results on the practical
manipulation of donor electrons in Si nanostructures.Comment: 8 pages, including 5 figures. v2: Minor clarifying changes in the
text and figures. Change of title. As published in PR
The Expression of Chemokines Is Downregulated in a Pre-Clinical Model of TTR V30M Amyloidosis
Inflammation is a hallmark of several neurodegenerative disorders including hereditary amyloidogenic transthyretin amyloidosis (ATTRv). ATTRv is an autosomal dominant neurodegenerative disorder with extracellular deposition of mutant transthyretin (TTR) aggregates and fibrils, particularly in nerves and ganglia of the peripheral nervous system. Nerve biopsies from ATTRv patients show increased cytokine production, but interestingly no immune inflammatory cellular infiltrate is observed around TTR aggregates. Here we show that as compared to Wild Type (WT) animals, the expression of several chemokines is highly downregulated in the peripheral nervous system of a mouse model of the disease. Interestingly, we found that stimulation of mouse Schwann cells (SCs) with WT TTR results in the secretion of several chemokines, a process that is mediated by toll-like receptor 4 (TLR4). In contrast, the secretion of all tested chemokines is compromised upon stimulation of SCs with mutant TTR (V30M), suggesting that V30M TTR fails to activate TLR4 signaling. Altogether, our data shed light into a previously unappreciated mechanism linking TTR activation of SCs and possibly underlying the lack of inflammatory response observed in the peripheral nervous system of ATTRv patients.The work was funded by the project Norte-01-0145-FEDER-000008 - Porto Neurosciences and Neurologic Disease Research Initiative at I3S, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (FEDER). JM was supported by FCT with a PhD fellowship SFRH/BD/129345/2017. MS is funded by FCT through Estı́mulo Individual ao Emprego Cientı́fico
HLA-DR in Cytotoxic T lymphocytes predicts breast cancer patients' response to neoadjuvant chemotherapy
Prediction of breast cancer response to Neoadjuvant Chemotherapy (NACT) is an urgent need to promptly direct non-responder patients to alternative therapies. Infiltrating T lymphocytes, namely cytotoxic T lymphocytes (CTLs) have been appointed as predictors of response. However, cancer cells have the ability to dampen CTLs' activity and thus, the prognostic value of the CTLs, per se, is debatable. Here, we disclose that more than the occurrence of CTLs, it is their activation state, revealed by HLA-DR expression, that can accurately predict response to NACT. Flow cytometry analysis of breast cancer biopsies showed that the frequency of CTLs and other lymphocytes were similar regardless disease stage and between NACT responders and non-responders. However, only breast cancer patients without axillary lymph node metastasis and NACT responders have HLA-DRhi CTLs. Interestingly, HLA-DR levels in tumor CTLs is correlated with HLA-DR levels in systemic CTLs. These HLA-DR+ CTLs produce IFN-γ and Granzyme B, enlightening their effector and probable anti-tumor activity profile. Moreover, the level of HLA-DR in CTLs is negatively correlated with the level of HLA-DR in T regulatory lymphocytes and with immunosuppressive and pro-tumor molecules in the tumor microenvironment. Hence, HLA-DR levels in CTLs is a highly sensitive and specific potential predictive factor of NACT-response, which can be assessed in blood to guide therapeutic decisions.Fundacao para a Ciencia e Tecnologia: PD/BD/114023/2015; PTDC/BBB-BMD/4497/2014. Liga Portuguesa Contra o Cancroinfo:eu-repo/semantics/publishedVersio
A prospective study demonstrating improved visualization when capsule endoscopy is performed after preparation with polyethylene glycol and ascorbic acid
Capsule endoscopy is used increasingly to obtain images of the gastrointestinal tract, yet it still remains unclear what is the best preparation for this type of exploration. Thus, the aim of this study was to compare the results of capsule endoscopy explorations performed after a basic preparation with a clear liquid diet, reduced iron intake and fasting or following preparation with a PEG/ascorbate solution. The results obtained from a prospective intervention group that used a PEG/ascorbate solution to prepare for capsule endoscopy were compared with those from a retrospective group of patients who followed the more basic preparation. The quality of visualization was assessed with the Park score, assessing visualization of the mucosal surface and the cleanliness of the intestinal lumen. The capsule transit time in different segments of the gastrointestinal tract was also evaluated. A significant improvement in the quality of small intestine visualization was observed in individuals prepared with the PEG/ascorbate solution as opposed to the basic preparation. Indeed, there were significant differences in the two separate components that contribute to the overall visualization score, with better mucosa visualization and lumen content scores in the intervention group, reflecting improved performance. The presence of diabetes appears to affect the results of these explorations, at least when employing the PEG/ascorbate preparation. As such, preparation with a PEG/ascorbate solution improves the results of capsule endoscopy when compared to a basic preparation, without the inconvenience of the more stringent preparations used for colonoscopies.info:eu-repo/semantics/publishedVersio
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