10 research outputs found
Kaon-Baryon Couplings and the Goldberger-Treiman Relation in SU(3) x SU(3)
The coupling constants G_(K N Lambda) and G_(K N Sigma) are obtained from the
Goldberger-Treiman relation in the strange channel with chiral symmetry
breaking taken into account. The results, G_(K N Lambda)=-12.3+-1.2 and G_(K N
Sigma)=5.5+-.5 come close to the SU(3) values.Comment: 6 Page
Couplings of the eta and eta' Mesons to the Nucleon
The couplings of the eta and eta' mesons to the nucleon are obtained from the
U_A(1) Goldberger-Treiman relation. The chiral symmetry breaking corrections
are very large and bring the calculated values of the coupling constants
G_etaNN and G_eta'NN close to values obtained from potential models.Comment: Version 3. The old version went by mistake Version to appear in Phys.
Lett.
QCD Sum Rule Determination of with Minimal Data Input
We present the results of a new evaluation of the running fine structure
constant at the scale of the mass in which the role of the
annihilation input data needed in this evaluation is minimized. This
is achieved by reducing the weight function in the
dispersion integral over the annihilation data by subtracting a
polynomial function from the weight function which mimics its energy dependence
in given energy intervals. In order to compensate for this subtraction the same
polynomial weight integral is added again but is now evaluated on a circular
contour in the complex plane using QCD and global duality. For the hadronic
contribution to the shift in the fine structure constant we obtain
. Adding in the
leptonic and top contributions our final result is .Comment: no changes, PostScript figures included in the text for convenienc
Chiral condensates from tau decay: a critical reappraisal
The saturation of QCD chiral sum rules is reanalyzed in view of the new and
complete analysis of the ALEPH experimental data on the difference between
vector and axial-vector correlators (V-A). Ordinary finite energy sum rules
(FESR) exhibit poor saturation up to energies below the tau-lepton mass. A
remarkable improvement is achieved by introducing pinched, as well as
minimizing polynomial integral kernels. Both methods are used to determine the
dimension d=6 and d=8 vacuum condensates in the Operator Product Expansion,
with the results: {O}_{6}=-(0.00226 \pm 0.00055) GeV^6, and O_8=-(0.0053 \pm
0.0033) GeV^8 from pinched FESR, and compatible values from the minimizing
polynomial FESR. Some higher dimensional condensates are also determined,
although we argue against extending the analysis beyond dimension d = 8. The
value of the finite remainder of the (V-A) correlator at zero momentum is also
redetermined: \Pi (0)= -4 \bar{L}_{10}=0.02579 \pm 0.00023. The stability and
precision of the predictions are significantly improved compared to earlier
calculations using the old ALEPH data. Finally, the role and limits of
applicability of the Operator Product Expansion in this channel are clarified.Comment: Replaced versio
Behavior of volatile compounds in membrane distillation: The case of carboxylic acids
International audienceThanks to its unique features, membrane distillation (MD) has been particularly applied for desalination but also for niches applications with feed solutions containing a mixture of volatile molecules. For such solutions, the complex interplay of the solutes and solvent physicochemical and operating parameters makes it challenging to predict the separation efficiency by MD. There is thus a need for a better understanding of the behavior of volatile compounds in MD as well as the influence of their physicochemical environment. This study aimed at investigating the influence of different operating parameters on rejection efficiency of air-gap MD towards carboxylic acids (formic, acetic and succinic acids). Acid rejection was found to be highly dependent on the carboxylic acid structure. In addition, it increased with the acid concentration, which could be related to the formation of acid dimers in the feed solution. This behavior is opposite to what is classically observed for pressure-driven membrane processes thus suggesting that MD can be a suitable alternative to these techniques for the concentration/separation of carboxylic acids. On the other hand, acid rejection decreased with the increase of feed temperature which could be explained by the calculation of the apparent energies of activation of both the water and carboxylic acids using an Arrhenius-type model. Finally, the acid dissociation rate played a key role in the acid rejection. Taking advantage of this observation, it was demonstrated how a simple pH adjustment can be used to successfully achieve the selective separation of ethanol (compared to acetic acid) from an acetic acid/ethanol aqueous mixture. © 2020 Elsevier B.V