Biomedical subjects

S J de Jong

Publications and source records attributed to S J de Jong.

10 recordsLinked to original sources

PubMed2004

Search for narrow tt resonances in pp collisions at square root of (s)=1.8 TeV.

A search for narrow resonances that decay into tt pairs has been performed using 130 pb(-1) of data in the lepton + jets channel collected by the Dphi detector in pp collisions at square root of (s)=1.8 TeV. There is no significant deviation observed from the standard-model predictions at a top-quark mass of 175 GeV/c2. We therefore present upper limits at the 95% confidence level on the product of the production cross section and branching fraction to tt for narrow resonances as a function of the resonance mass MX. These limits are used to exclude the existence of a leptophobic top-color particle with mass MX<560 GeV/c2, using a theoretical cross section for a width GammaX=0.012MX.

Journal Article↗

PubMed2003

Search for large extra dimensions in the monojet+E(T) channel with the DØ detector.

We present a search for large extra dimensions (ED) in pp collisions at a center-of-mass energy of 1.8 TeV using data collected by the DØ detector at the Fermilab Tevatron in 1994-1996. Data corresponding to 78.8+/-3.9 pb(-1) are examined for events with large missing transverse energy, one high-p(T) jet, and no isolated muons. There is no excess observed beyond expectation from the standard model, and we place lower limits on the fundamental Planck scale of 1.0 and 0.6 TeV for 2 and 7 ED, respectively.

Journal Article↗

PubMed2002

Search for R-parity violating supersymmetry in two-muon and four-jet topologies.

We present results of a search for R-parity-violating decay of the neutralino chi;01, taken as the lightest supersymmetric particle, to a muon and two jets. The decay proceeds through a lepton-number violating coupling lambda(')(2jk) (j=1,2; k=1,2,3), with R-parity conservation in all other production and decay processes. In the absence of candidate events from 77.5+/-3.9 pb(-1) of data collected by the D0 experiment at the Fermilab Tevatron in pp collisions at sqrt[s]=1.8 TeV, and with an expected background of 0.18+/-0.03+/-0.02 events, we set limits on squark and gluino masses within the framework of the minimal low-energy supergravity-supersymmetry model.

Journal Article↗

PubMed2002

Direct search for charged higgs bosons in decays of top quarks.

We present a search for charged Higgs bosons in decays of pair-produced top quarks in pp collisions at sqrt[s] = 1.8 TeV recorded by the D0 detector at the Fermilab Tevatron collider. With no evidence for signal, we exclude most regions of the ( M(H+/-),tan(beta)) parameter space where the decay t--> H(+)b has a branching fraction >0.36 and B(H+/--->tau(nu)(tau)) is large.

Journal Article↗

PubMed2001

Ratio of isolated photon cross sections in pp macro collisions at square root of s = 630 and 1800 GeV.

The inclusive cross section for production of isolated photons has been measured in pp macro collisions at square root of s = 630 GeV with the D0 detector at the Fermilab Tevatron Collider. The photons span a transverse energy (E(T)) range from 7-49 GeV and have pseudorapidity absolute value of eta < 2.5. This measurement is combined with the previous D0 result at square root of s = 1800 GeV to form a ratio of the cross sections. Comparison of next-to-leading-order QCD with the measured cross section at 630 GeV and the ratio of cross sections show satisfactory agreement in most of the E(T) range.

Journal Article↗

PubMed2001

Search for new physics using QUAERO: a general interface to D0 event data.

We describe QUAERO, a method that (i) enables the automatic optimization of searches for physics beyond the standard model, and (ii) provides a mechanism for making high energy collider data generally available. We apply QUAERO to searches for standard model WW, ZZ, and t t macro production, to searches for these objects produced through a new heavy resonance, and to the first direct search for W'-->WZ. Through this interface, we make three data sets collected by the D0 experiment at square root of [s] = 1.8 TeV publicly available.

Journal Article↗

PubMed2001

Search for heavy particles decaying into electron-positron pairs in pp collisions.

We present results of searches for technirho (rho(T)), techniomega (omega(T)), and Z' particles, using the decay channels rho(T),omega(T),Z'-->e(+)e(-). The search is based on 124.8 pb(-1) of data collected by the D0 detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes pp-->rho(T),omega(T),Z'-->e(+)e(-) as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate rho(T) and omega(T) states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermions as the Z boson.

Journal Article↗

PubMed2001

Biodegradable hydrogels based on stereocomplex formation between lactic acid oligomers grafted to dextran.

A novel hydrogel system in which crosslinking is established by stereocomplex formation between lactic acid oligomers of opposite chirality is proposed. To investigate the feasibility of this novel system, we first investigate whether there is an operation window where lactic acid oligomers in either the D- or L-form do not give a crystalline phase, whereas in a blend of the D- and L-form stereocomplex formation occurs. Therefore, D- and L-lactic acid oligomers with different degrees of polymerization (DP) were prepared and analyzed using DSC. It was shown that crystallinity was present in D- or L-oligomers with DP > or = 11. On the other hand, in blends of D- and L-oligomers of lactic acid crystallinity (stereocomplexation) was already observed at a DP > or = 7. In the next step, L- and D-lactic acid oligomers were coupled via their terminal hydroxyl group to dextran, yielding dex-(L)lactate and dex-(D)lactate, respectively. Upon dissolving each product in water separately and mixing the solutions, a hydrogel is formed at room temperature as demonstrated by rheological measurements. The storage modulus of the obtained hydrogel strongly decreased upon heating to 80 degrees C, while it was restored upon cooling to 20 degrees C demonstrating the thermo-reversibility and the physical nature of the cross-links. The storage modulus of the gels depends on the degree of polymerization of the lactate acid grafts and their degree of substitution on dextran. Interestingly, gel formation was favored when one lactic oligomer was coupled via its hydroxyl group whereas the oligomer of opposite chirality was coupled via its carboxylic acid group. This is ascribed to the parallel packing of the oligomers in stereocomplexes.

Calorimetry, Differential Scanning↗

PubMed2001

Physically crosslinked dextran hydrogels by stereocomplex formation of lactic acid oligomers: degradation and protein release behavior.

Hydrogels, physically crosslinked through stereocomplex formation, were obtained by mixing aqueous solutions of dextran with L-lactic acid grafts and dextran with D-lactic acid grafts. Protein-loaded hydrogels were simply prepared by dissolving the protein in these dextran solutions prior to mixing. It was shown that under physiological conditions the gels are fully degradable. When the gels were exposed to an aqueous buffer solution, they first showed a swelling phase in which their weight increased 2-3 times due to absorption of water, followed by a dissolution phase. The degradation time depended on the composition of the hydrogel, i.e., the number of lactate grafts, the length and polydispersity of the grafts and the initial water content, and varied from 1 to 7 days. Most likely, the degradation of the stereocomplex hydrogel started with hydrolysis of the carbonate ester, which links the lactate graft to dextran. The gels showed a release of the entrapped model proteins (IgG and lysozyme) over 6 days and the kinetics depended on the gel characteristics, such as the polydispersity of the lactate grafts and the initial water content. Lysozyme was mainly released by Fickian diffusion, indicating that its hydrodynamic diameter is smaller than the hydrogel mesh size. On the other hand the release of IgG was governed by diffusion as well as swelling/degradation of the hydrogel. Importantly, the proteins were quantitatively released from the gels and with full preservation of the enzymatic activity of lysozyme, emphasizing the protein-friendly preparation method of the protein-loaded stereocomplex hydrogel.

Algorithms↗

PubMed1993

Changes in life-style in men under sixty years of age before and after acute myocardial infarction: a case-control study.

A case-control study was conducted to examine the presence of psychosocial factors before, during, and after acute myocardial infarction (AMI) in Dutch men under sixty years of age. The study included 42 AMI patients and 48 individuals in an age-adjusted sampled control group. The psychological factors included high level of psychological stress, of social isolation, type A1 and A2 behavior, and mental depression. They were assessed by means of the Health Insurance Questionnaire of Greater New York. Univariate analysis indicated that the presence of psychological factors was common at the onset of the myocardial infarction (MI). It clearly diminished, however, after the MI had taken place. In a stepwise logistic regression analysis after adjustment for the independent variables hypertension, cholesterol, and smoking, the following three characteristics were independently related to the risk of MI: no talking (item of social isolation, P = 0.008), need to excel (item of type A1 behavior, P = 0.04), and blue feeling (item of mental depression, P = 0.09). The authors conclude that in men under 60 with AMI, the presence of psychosocial characteristics is common and that this group is going to change its life-style soon after the MI, even without any psychosocial rehabilitation therapy. Follow-up studies investigating the influence of psychological factors on survival and reinfarction should be adjusted for these changes in life-style.

Adult↗