20 research outputs found
Design, Commissioning and Performance of the PIBETA Detector at PSI
We describe the design, construction and performance of the PIBETA detector
built for the precise measurement of the branching ratio of pion beta decay,
pi+ -> pi0 e+ nu, at the Paul Scherrer Institute. The central part of the
detector is a 240-module spherical pure CsI calorimeter covering 3*pi sr solid
angle. The calorimeter is supplemented with an active collimator/beam degrader
system, an active segmented plastic target, a pair of low-mass cylindrical wire
chambers and a 20-element cylindrical plastic scintillator hodoscope. The whole
detector system is housed inside a temperature-controlled lead brick enclosure
which in turn is lined with cosmic muon plastic veto counters. Commissioning
and calibration data were taken during two three-month beam periods in
1999/2000 with pi+ stopping rates between 1.3*E3 pi+/s and 1.3*E6 pi+/s. We
examine the timing, energy and angular detector resolution for photons,
positrons and protons in the energy range of 5-150 MeV, as well as the response
of the detector to cosmic muons. We illustrate the detector signatures for the
assorted rare pion and muon decays and their associated backgrounds.Comment: 117 pages, 48 Postscript figures, 5 tables, Elsevier LaTeX, submitted
to Nucl. Instrum. Meth.
Helianthus tuberosus and polyamine research: past and recent applications of a classical growth model
The earlieststudiesconcerningpolyamines(PAs)inplantswereperformedbyusing in vitro cultured
explantsof Helianthustuberosus dormanttuber.Thisparenchymatissuewasparticularlyusefulduetoits
susceptibility toseveralgrowthsubstances,includingPAs.Duringtuberdormancy,PAlevelsaretoolowto
sustaincelldivision;thus Helianthus representsanaturalPA-deficient model.Whencultivated in vitro in
the presenceofauxins, Helianthus tuber dormantparenchymacellsattheG0 stage starttodivide
synchronously acquiringmeristematiccharacteristics.Therequirementforauxinstoinducecelldivision
can besubstitutedbyaliphaticPAssuchasputrescine,spermidineorspermine.Cylindersorslicesof
explantedhomogeneoustuberparenchymawereculturedinliquidmediumforshort-termstudiesonthe
cell cycle,oronsolidagarmediumforlong-termexperiments.Morphologicalandphysiologicalmodificationsofsynchronouslydividingcellswerestudiedduringthedifferentphasesofthecellcycleinrelat
on
to PAsbiosynthesisandoxidation.Long-termexperimentsledtotheidentification ofthePAsasplant
growthregulators,asthesolenitrogensource,astuberstoragesubstancesandasessentialfactorsfor
morphogeneticprocessesandcellhomeostasis.Morerecentlythissystemwasusedtostudytheeffectson
plant cellproliferationofplatinum-orpalladium-deriveddrugs(cisplatinandplatinumorpalladiumbi-
substitutedspermine)thatareusedinhumancancercelllinesasantiproliferativeandcytotoxicagents.
CisplatinwasthemostactivebothincellproliferationinhibitionandonPAmetabolism.Similarexperi-
ments wereperformedusingthreeagmatineanalogous.Differenteffectsofthesecompoundswere
observedoncellproliferation,freePAlevelsandenzymeactivities,leadingtoahypothesisofacorrelation
between theirchemicalstructureandtheagmatinemetabolisminplant