Source and quantity of carbon influence its sequestration in Rostherne Mere (UK) sediment: a novel application of stepped combustion radiocarbon analysis

We explored the roles of phytoplankton production, carbon source, and human activity on carbon accumulation in a eutrophic lake (Rostherne Mere, UK) to understand how changes in nutrient loading, algal community structure and catchment management can influence carbon sequestration in lake sediments. Water samples (dissolved inorganic, organic and particulate carbon) were analysed to investigate contemporary carbon sources. Multiple variables in a 55-cm sediment core, which represents the last ~ 90 years of accumulation, were studied to determine historical production rates of algal communities and carbon sources. Fluctuations in net primary production, inferred from sedimentary diatom abundance and high-performance liquid chromatography (HPLC) pigment methods, were linked to nutrient input from sewage treatment works (STW) in the catchment. Stepped combustion radiocarbon (SCR) measurements established that lake sediment contains between 11% (~ 1929 CE) and 69% (~ 1978 CE) recalcitrant carbon, with changes in carbon character coinciding with peaks in accumulation rate and linked to STW inputs. Catchment disturbance was identified by radiocarbon analysis, and included STW construction in the 1930s, determined using SCR analysis, and recent nearby highway construction, determined by measurements on dissolved organic carbon from the lake and outflow river. The quantity of autochthonous carbon buried was related to diatom biovolume accumulation rate (DBAR) and decreased when diatom accumulation rate and valve size declined, despite an overall increase in net carbon production. HPLC pigment analysis indicated that changes in total C deposition and diatom accumulation were related to proliferation of non-siliceous algae. HPLC results also indicated that dominance of recalcitrant carbon in sediment organic carbon was likely caused by increased deposition rather than preservation factors. The total algal accumulation rate controlled the sediment organic carbon accumulation rate, whereas DBAR was correlated to the proportion of each carbon source buried

Quantitative optical spectroscopy of 87^{87}Rb vapour in the Voigt geometry in DC magnetic fields up to 0.4T

We present a detailed spectroscopic investigation of a thermal ⁸⁷Rb atomic vapour in magnetic fields up to 0.4T in the Voigt geometry. We fit experimental spectra with our theoretical model ElecSus and find excellent quantitative agreement, with RMS errors of backsim0.3%. We extract the magnetic field strength and the angle between the polarisation of the light and the magnetic field from the atomic signal and find excellent agreement to within backsim1% with a commercial Hall probe. Finally, we present an investigation of the relative sensitivity of this technique to variations in the field strength and angle with a view to enabling atom-based high-field vector magnetometry

Source and quantity of carbon influence its sequestration in Rostherne Mere (UK) sediment: a novel application of stepped combustion radiocarbon analysis

We explored the roles of phytoplankton production, carbon source, and human activity on carbon accumulation in a eutrophic lake (Rostherne Mere, UK) to understand how changes in nutrient loading, algal community structure and catchment management can influence carbon sequestration in lake sediments. Water samples (dissolved inorganic, organic and particulate carbon) were analysed to investigate contemporary carbon sources. Multiple variables in a 55-cm sediment core, which represents the last ~ 90 years of accumulation, were studied to determine historical production rates of algal communities and carbon sources. Fluctuations in net primary production, inferred from sedimentary diatom abundance and high-performance liquid chromatography (HPLC) pigment methods, were linked to nutrient input from sewage treatment works (STW) in the catchment. Stepped combustion radiocarbon (SCR) measurements established that lake sediment contains between 11% (~ 1929 CE) and 69% (~ 1978 CE) recalcitrant carbon, with changes in carbon character coinciding with peaks in accumulation rate and linked to STW inputs. Catchment disturbance was identified by radiocarbon analysis, and included STW construction in the 1930s, determined using SCR analysis, and recent nearby highway construction, determined by measurements on dissolved organic carbon from the lake and outflow river. The quantity of autochthonous carbon buried was related to diatom biovolume accumulation rate (DBAR) and decreased when diatom accumulation rate and valve size declined, despite an overall increase in net carbon production. HPLC pigment analysis indicated that changes in total C deposition and diatom accumulation were related to proliferation of non-siliceous algae. HPLC results also indicated that dominance of recalcitrant carbon in sediment organic carbon was likely caused by increased deposition rather than preservation factors. The total algal accumulation rate controlled the sediment organic carbon accumulation rate, whereas DBAR was correlated to the proportion of each carbon source buried

Performance of the LHCb vertex locator

The Vertex Locator (VELO) is a silicon microstrip detector that surrounds the proton-proton interaction region in the LHCb experiment. The performance of the detector during the first years of its physics operation is reviewed. The system is operated in vacuum, uses a bi-phase CO2 cooling system, and the sensors are moved to 7 mm from the LHC beam for physics data taking. The performance and stability of these characteristic features of the detector are described, and details of the material budget are given. The calibration of the timing and the data processing algorithms that are implemented in FPGAs are described. The system performance is fully characterised. The sensors have a signal to noise ratio of approximately 20 and a best hit resolution of 4 μm is achieved at the optimal track angle. The typical detector occupancy for minimum bias events in standard operating conditions in 2011 is around 0.5%, and the detector has less than 1% of faulty strips. The proximity of the detector to the beam means that the inner regions of the n+-on-n sensors have undergone space-charge sign inversion due to radiation damage. The VELO performance parameters that drive the experiment's physics sensitivity are also given. The track finding efficiency of the VELO is typically above 98% and the modules have been aligned to a precision of 1 μm for translations in the plane transverse to the beam. A primary vertex resolution of 13 μm in the transverse plane and 71 μm along the beam axis is achieved for vertices with 25 tracks. An impact parameter resolution of less than 35 μm is achieved for particles with transverse momentum greater than 1 GeV/c

Precision luminosity measurements at LHCb

Measuring cross-sections at the LHC requires the luminosity to be determined accurately at each centre-of-mass energy √s. In this paper results are reported from the luminosity calibrations carried out at the LHC interaction point 8 with the LHCb detector for √s = 2.76, 7 and 8 TeV (proton-proton collisions) and for √sNN = 5 TeV (proton-lead collisions). Both the "van der Meer scan" and "beam-gas imaging" luminosity calibration methods were employed. It is observed that the beam density profile cannot always be described by a function that is factorizable in the two transverse coordinates. The introduction of a two-dimensional description of the beams improves significantly the consistency of the results. For proton-proton interactions at √s = 8 TeV a relative precision of the luminosity calibration of 1.47% is obtained using van der Meer scans and 1.43% using beam-gas imaging, resulting in a combined precision of 1.12%. Applying the calibration to the full data set determines the luminosity with a precision of 1.16%. This represents the most precise luminosity measurement achieved so far at a bunched-beam hadron collider

Search for supersymmetry in hadronic final states with missing transverse energy using the variables αT and b-quark multiplicity in pp collisions at [Formula: see text].

An inclusive search for supersymmetric processes that produce final states with jets and missing transverse energy is performed in pp collisions at a centre-of-mass energy of 8 TeV. The data sample corresponds to an integrated luminosity of 11.7 fb-1 collected by the CMS experiment at the LHC. In this search, a dimensionless kinematic variable, αT, is used to discriminate between events with genuine and misreconstructed missing transverse energy. The search is based on an examination of the number of reconstructed jets per event, the scalar sum of transverse energies of these jets, and the number of these jets identified as originating from bottom quarks. No significant excess of events over the standard model expectation is found. Exclusion limits are set in the parameter space of simplified models, with a special emphasis on both compressed-spectrum scenarios and direct or gluino-induced production of third-generation squarks. For the case of gluino-mediated squark production, gluino masses up to 950-1125 GeV are excluded depending on the assumed model. For the direct pair-production of squarks, masses up to 450 GeV are excluded for a single light first- or second-generation squark, increasing to 600 GeV for bottom squarks

Probing color coherence effects in pp collisions at [Formula: see text].

A study of color coherence effects in pp collisions at a center-of-mass energy of 7[Formula: see text] is presented. The data used in the analysis were collected in 2010 with the CMS detector at the LHC and correspond to an integrated luminosity of 36 pb[Formula: see text]. Events are selected that contain at least three jets and where the two jets with the largest transverse momentum exhibit a back-to-back topology. The measured angular correlation between the second- and third-leading jet is shown to be sensitive to color coherence effects, and is compared to the predictions of Monte Carlo models with various implementations of color coherence. None of the models describe the data satisfactorily

Performance of photon reconstruction and identification with the CMS detector in proton-proton collisions at √s = 8 TeV

A description is provided of the performance of the CMS detector for photon reconstruction and identification in proton-proton collisions at a centre-of-mass energy of 8 TeV at the CERN LHC. Details are given on the reconstruction of photons from energy deposits in the electromagnetic calorimeter (ECAL) and the extraction of photon energy estimates. The reconstruction of electron tracks from photons that convert to electrons in the CMS tracker is also described, as is the optimization of the photon energy reconstruction and its accurate modelling in simulation, in the analysis of the Higgs boson decay into two photons. In the barrel section of the ECAL, an energy resolution of about 1% is achieved for unconverted or late-converting photons from Hγγ decays. Different photon identification methods are discussed and their corresponding selection efficiencies in data are compared with those found in simulated events

Measurement of jet multiplicity distributions in [Formula: see text] production in pp collisions at [Formula: see text].

The normalised differential top quark-antiquark production cross section is measured as a function of the jet multiplicity in proton-proton collisions at a centre-of-mass energy of 7[Formula: see text] at the LHC with the CMS detector. The measurement is performed in both the dilepton and lepton+jets decay channels using data corresponding to an integrated luminosity of 5.0[Formula: see text]. Using a procedure to associate jets to decay products of the top quarks, the differential cross section of the [Formula: see text] production is determined as a function of the additional jet multiplicity in the lepton+jets channel. Furthermore, the fraction of events with no additional jets is measured in the dilepton channel, as a function of the threshold on the jet transverse momentum. The measurements are compared with predictions from perturbative quantum chromodynamics and no significant deviations are observed