Abstract: A data acquisition system and method are described that may be used with various spectrometers. The data acquisition system may include an ion detector and a processing circuit. The processing circuit may include an initial processing module and a spectra processing module. According to one embodiment, the spectra processing module generates stick spectra and supplies the stick spectra to an external processor. The stick spectra comprise a peak intensity, resolution, and a location in the spectra for each detected peak. The initial processing module may contiguously sample the ion detection signals at a rate matched to the capabilities of the ion detector (up to at least 1.5 GHz) over a full spectral range. The spectra processing module may receive the processed signals and generate spectra from the processed signals at a rate matched to the time response of the separation techniques (up to 200 spectra/second).

Abstract: Disclosed are methods for recalibrating mass spectrometry data that provide improvement in both mass accuracy and precision by adjusting for experimental variance in parameters that have a substantial impact on mass measurement accuracy. Optimal coefficients are determined using correlated pairs of mass values compiled by matching sets of measured and putative mass values that minimize overall effective mass error and mass error spread. Coefficients are subsequently used to correct mass values for peaks detected in the measured dataset, providing recalibration thereof. Sub-ppm mass measurement accuracy has been demonstrated on a complex fungal proteome after recalibration, providing improved confidence for peptide identifications.

Abstract: A method for discriminating particle groups comprises generating, by a particle analyzer, a particle characteristic distribution histogram in which the abscissa indicates respective channels for representing the characteristics of the particles, and the ordinate indicates the particle count; setting a valid area selection height in the particle characteristics distribution histogram; and generating an equivalent negative histogram based on the set height and the particle characteristic distribution histogram.

Abstract: A method for obtaining at least one calibration filter for a Mass Spectrometry (MS) instrument system. Measured isotope peak cluster data in a mass spectral range is obtained for a given calibration standard. Relative isotope abundances and actual mass locations of isotopes corresponding thereto are calculated for the given calibration standard. Mass spectral target peak shape functions centered within respective mass spectral ranges are specified. Convolution operations are performed between the calculated relative isotope abundances and the mass spectral target peak shape functions to form calculated isotope peak cluster data. A deconvolution operation is performed between the measured isotope peak cluster data and the calculated isotope peak cluster data after the convolution operations to obtain the at least one calibration filter. Provisions are made for normalizing peak widths, combining internal and external calibration, and using selected measured peaks as standards.

Abstract: The spectral method for determining the concentrations of a substance in a mixture of any number of substances is defined by a chemical image having a plurality of pixels (520). The method includes steps of providing a spectrum for each of the number of substances in the mixture (530), and obtaining the spectrum for one of the plurality of pixels, and calculating a plurality of estimated concentrations of each substance in the mixture as a function of the spectrum for each substance and the spectrum for the pixel, and calculating a deviation value for each of the plurality of estimated concentrations as a function of the spectrum of each of the number of substances in the mixture, and selecting the estimated concentration with the lowest deviation factor as a most likely concentration of each substance in the mixture (550).

Abstract: The present invention achieves a mass analysis method that can identify protein or peptide with high speed and high sensitivity. A mass spectrum is obtained from a standard sample of healthy person, an ion is selected from the mass spectrum as a precursor ion, and a mass spectrum of the precursor ion is obtained [(a) to (d)]. A mass spectrum is obtained from a sample of interest to be measured of patient, an ion other than the precursor ion of the standard sample is selected from the mass spectrum as a precursor ion, and a mass spectrum of the precursor ion is obtained [(g) to (k)]. Identifications on peptide/protein specific to the standard sample and the sample to be measured, and common to both are conducted [(r) to (q)], and based on the results, comparative analysis on peptide/protein of the sample to be measured (t).

Abstract: The invention relates to a device and a process for nucleophilic fluorination of a substance, especially for synthesis of an 18F-labeled substance for examination using a positron emission tomograph. The device comprises an anion exchange device (102) for extraction of [18F]fluoride ions by means of adsorption from a target fluid, whereby the anion exchange device (102) can be charged via a supply device (101) with the target fluid; and a measurement device (104) with a measurement chamber (103) for measuring initial radioactivity of the [18F]fluoride ions, the anion exchange device (102) being arranged at least partially in the measurement chamber (103) of the measurement device (104).

Abstract: Provided is a method of controlling a photolithography cluster or a subsequent fabrication cluster using optical metrology to determine profile parameters of a photomask structure covered with a pellicle. An optical metrology model of the pellicle is developed and integrated with the optical metrology model of the photomask structure. The optical metrology model of the photomask taking into account the optical effects on the illumination and detection beams transmitted through the pellicle and diffracted by the photomask structure. One or more profile parameters of the photomask structure is determined and used to adjust one or more process parameters or equipment settings of a photolithography cluster using the photomask or a subsequent fabrication cluster.

Abstract: The present invention provides a distributed sensing system in a networked environment for identifying an analyte, including a first sensor array connected to the network comprising sensors capable of producing a first response in the presence of a chemical stimulus; a second sensor array connected to the network comprising sensors capable of producing a second response in the presence of a physical stimulus; and a computer comprising a resident algorithm. The algorithm indicates or selects the most relevant sensor in the network to identify the analyte. The sensors can be separated over large spatial areas, wherein the sensor arrays are networked. Suitable networks include a computer local area network, an intranet or the Internet.

Abstract: A fluroescene detecting device irradiates an object to be measured with a laser beam, receives fluroescene generated from the object and processes a fluorescence signal generated when receiving the fluroescene. The device includes a laser light source section outputting the laser beam for irradiating the object, a light receiving section outputting the fluorescene signal of the fluorescene generated by the irradiated object, a light source control section generates a modulatioon signal having a frequency in order to time-modulate an intensity of the laser beam, and a processing section that calculates a flurescene relaxation time of the fluorescene of the object based on the fluorescene relaxation time of the fluorescene of the object based on the fluorescene relaxation time of the fluorescene of the object based on the fluorescene signal output from the light receiving section.

Abstract: A method is proposed for detecting at least one chemical compound V contained in a medium (312). The method comprises a verification step (420) which is used to determine whether V is contained in the medium (312). The method furthermore comprises an analysis step (424) in which a concentration c of the at least one chemical compound V is determined.

Abstract: Bias plays an important role in factor analysis and is often implicitly made use of, for example, to constrain solutions to factors that conform to physical reality. However, when components are collinear, a large range of solutions may exist that satisfy the basic constraints and fit the data equally well. In such cases, the introduction of mathematical bias through the application of constraints may select solutions that are less than optimal. The biased alternating least squares algorithm of the present invention can offset mathematical bias introduced by constraints in the standard alternating least squares analysis to achieve factor solutions that are most consistent with physical reality. In addition, these methods can be used to explicitly exploit bias to provide alternative views and provide additional insights into spectral data sets.

Abstract: The present invention relates to methods for extracting qualitative and quantitative information from natural ingredient mixtures, utilizing two or more data sets and newly developed chemometric method known as improved alternative moving window factor analysis (IAMWFA).

Abstract: Various technologies are described by which the usable portion or threshold value of a sigmoid curve is found. Such techniques can be useful, for example, when determining the concentration or presence of a substance in a test sample. Various techniques can avoid variability in results.

Abstract: Methods and apparatus for providing data processing and control for use in a medical communication system are provided.

Abstract: Methods and apparatus for providing data processing and control for use in a medical communication system are provided.

Abstract: A method for verifying carbon storage in seawater to which a growth stimulant has been supplied for stimulating a bloom of nitrogen fixing organisms for enhancing carbon storage therein, comprises selecting a region of seawater including a surface mixed layer, a euphotic zone extending below the surface mixed layer, and a plurality of deeper zones; determining the effect of growth stimulant on the rate of nitrogen fixation and carbon transport in the region; and determining the amount of carbon stored at different depths and projected duration of carbon storage at each of the depths.

Abstract: A method of establishing liquid classes of complex mixtures for liquid handling equipment. The mixtures are composed of components and the equipment has equipment parameters. The first step comprises preparing a response curve for the components. The next step comprises using the response curve to prepare a response indicator for the mixtures. The next step comprises deriving a model that relates the components and the mixtures to establish the liquid classes.

Abstract: A method of determining an empirical formula of an analyte ion from a measured mass spectrum including a main peak and one or more isotope peaks. The method comprises comparing a relative isotopic intensity of the measured isotope peak to a calculated relative isotopic intensity of an isotopic ion of a proposed empirical formula and comparing a relative mass defect of the measured isotope peak to a calculated relative mass defect of the isotopic ion of the proposed empirical formula. The proposed empirical formula is identified as a potential candidate for the analyte ion based on these comparisons.

Abstract: A mass spectrometer comprises an ion detector, an analog-to-digital (A/D) converter, a sample adjuster, and an adder. The A/D converter is configured to generate digital samples representing an analog signal received from the ion detector during a mass scan. The adder is configured to sum the samples with corresponding unsuppressed samples representing analog signals received from the ion detector during previous mass scans, the summed samples defining a mass spectrum. The sample adjuster is configured to identify a peak defined by the samples and to suppress all but one of the samples defining the identified peak to enhance resolution of a peak in the mass spectrum.

Abstract: The present invention relates to the three dimensional solution structure of the N-terminal domain of TNFR-1 associated death domain protein (“N-TRADD”), as well as the identification and characterization of a C-TRAF2 binding active site of N-TRADD. Also provided for by the present invention are methods of utilizing the three dimensional structures for the design and selection of potent and selective inhibitors of TNF signaling pathways.

Abstract: A method for estimating the concentration of a particular gas in a gas mixture having a fluctuating pressure is provided. A sensor output signal indicating the concentration of a particular gas in the gas mixture is received from a gas sensor. The received sensor output signal may vary over time due to the fluctuating pressure of the gas mixture. The received sensor output signal may be processed to determine an estimate of the concentration of the particular gas in the gas mixture. The processing may include performing an autocorrelation of the signal. In some embodiments, the particular gas is oxygen and the method is used to estimate the concentration of oxygen in a gas mixture having a fluctuating pressure.

Abstract: Methods and apparatus for providing data processing and control for use in a medical communication system are provided.

Abstract: A multiphase flow meter and data system including a volumetric flow meter, a multiphase density sensor, and a data center interconnected to the volumetric flow meter, and the multiphase density sensor. The multiphase density sensor has piping with a first transition section, a non-conductive section, and a second transition section. Two conductive plates are externally mounted to the non-conductive section, thereby forming a capacitor. The multiphase flow meter and data system provides a way to measure the percentages of water, gas, and/or crude oil that flow in a pipeline without the separation of phases on-line and in real time. The multiphase flow meter and data system allows reliable real-time measurement with the possibility to transmit results to a remote location without the presence of a technician at the measuring site.

Abstract: A biosensor with multi-channel A/D conversion and a method thereof are provided. The present biosensor includes a chip generating a time-dependent analog signal in response to a content of a specific component of a specimen provided thereon, a multi-channel A/D converter, and a microprocessor. The multi-channel A/D converter has multiple channels simultaneously receiving the time-dependent analog signal in each sampling interval to convert the time-dependent analog signal to a set of digital signals. The microprocessor receives the sets of digital signals in a period of sampling time and determines the content of the specific component based on the sets of digital signals. The present biosensor provides a multi-channel A/D conversion for the time-dependent analog signal to improve the resolution of the determination of the content of the specific component.

Abstract: The invention relates to the acquisition of mass spectra of complex protein mixtures, often called protein profiles, for example to search for biomarkers which indicate stress situations, or to identify microbes. Up to now protein profiles have been acquired using ionization by matrix-assisted laser desorption with high detection sensitivity in linear time-of-flight mass spectrometers, but these display very poor mass resolution and a very poor reproducibility of the mass values. The invention provides methods which produce surprisingly similar mass spectra, but with far higher mass resolution and mass accuracy. Ionization takes place outside the vacuum at ambient pressure, preferably by means of laser desorption and CI post-ionization. Analysis of the ions takes place in a high-resolution mass spectrometer, for example a reflector time-of-flight mass spectrometer with orthogonal ion injection.

Abstract: A system for sensing a presence and/or a concentration of a target substance in a fluid has a sensor and a processor coupled to the sensor. The sensor has a test probe having at least first and second test electrodes, wherein at least the first test electrode is functionalized to create a permittivity change in the area between the first and second test electrodes in the presence of the target substance. The sensor also has a reference probe having at least first and second reference electrodes. The processor is configured to determine at least one permittivity-based metric for the test probe; determine the at least one permittivity-based metric for the reference probe; and determine the presence and/or the concentration of the target substance based on the at least one permittivity-based metric for the test probe and the at least one permittivity-based metric for the reference probe. Related methods are disclosed.

Abstract: An automated or fully automated mass spectral system and a method of operating the system to identify a sample ion or compound. The system includes at least one computer addressable holder for at least one of standard and sample; at least one mass spectrometer configured to acquire one of continuum, profile, and raw mode mass spectral data; a computer system including a first software component to control introduction of at least one of the sample and the standard, data acquisition, and data analysis; a second software component for performing a mass spectral calibration involving at least m/z value, to report at least one of accurate mass, a list of possible elemental compositions, and a measurement statistic; and a third software component capable of acting on reported result or measurement statistic to change at least one of the introduction of at least one of the sample and the standard, data acquisition, data analysis, reported result, and measurement statistic.

Abstract: A modular reader system and method provides for testing a test sample and determining characteristics of the sample. A first test module is configured to perform a first reading on a test sample and produce data regarding the reading. A second test module is configured to perform a second reading of the test sample and produce data regarding the second reading. The first and second test modules are communicatively coupled to a control module. The control module collects the data produced by the first and second test modules and processes the data to determine characteristics of the test sample.

Abstract: The disclosed technology relates to the analysis of dissociation spectrum data that includes spectral peaks that represent fragments of a parent ion. The parent ion includes molecular subunits that are connected at cleavage sites. The technology accesses the dissociation spectrum data and determines a reference mass of one of the fragments where at least one of the molecular subunits in the fragment is unknown. The technology also selects a candidate parent ion description from a database of molecule descriptions where a computed ion mass of the candidate parent ion description matches the reference mass and scores the candidate parent ion description.

Abstract: The system and method provide security and cargo handling personnel a versatile tool to rapidly check cargo for hidden radiological materials, explosives, drugs, and chemical weapons material. Gamma ray emission is stimulated by a pulsed neutron source. The gamma ray signature is used to classify the material. Passive gamma ray analysis can be used to detect and identify radiological material. The method of determining the contents of a target includes irradiating a target; detecting at least one spectrum emitted from the target; performing a primary analysis to extract a first set of indicators; and performing a secondary analysis to decide the contents of the target. The primary analysis utilizes either a least squares analysis or principal component analysis. The secondary analysis utilizes a generalized likelihood ratio test or support vector machines.

Abstract: The invention relates to a powder dispensing device for dispensing powder into hard gelatin capsules or the like. The powder dispensing device comprises at least one plunger for compacting the powder to a powder compact and/or at least one transfer plunger which transfers the previously produced powder compact into a capsule part ready to be filled. The device includes a sensing apparatus including fiber-optical cables and a lens for introducing and receiving radiation passed through the powder or the powder compact. The sensing apparatus is connected to either the compacting plunger or the transfer plunger, or both.

Abstract: A method for characterizing a sample containing at least one compound, preferably a biological sample comprising at least one metabolite, is proposed. In a first process step, a three-dimensional first set of data is generated by analyzing the sample by using at least one time resolved separation technique (214) and at least mass one resolved separation technique (216). The set of data comprises at least one signal I as a function of a mass variable over a first range of measurement (420) and of a time variable over a second range of measurement (422). In a second process step, the first range of measurement (420) is divided into at least two mass variable intervals (424). For each mass variable interval (424), an extracted signal is selected, wherein the extracted signal is a function of the time variable. In a third process step, the second range of measurement (422) is divided into at least one time variable interval (426).

Abstract: The present invention is designed to efficiently calculate isotopic distribution in order to simulate mass spectra data for any chemical compound of interest. The simulated spectra considers the various isotopes of the compound based upon a probability calculation that takes into consideration the natural abundance of each isotope of individual elements of the compound. The probability calculation generates a relative probability associated with each isotope species of the subject compound. The simulated spectra are displayed on an x-y coordinate illustrating the calculated formula weight on the abscissa (x-axis) and the intensity of the specific species on the ordinate (y-axis). This theoretical data is then compared to experimental data taken from a mass spectrometer in order to identify the chemical compound at issue.

Abstract: The concentration of air or other agents in a fluid delivery line is determined by monitoring agent signals and processing those agent signals along with information regarding the age of each agent signal. The processor determines a primary agent concentration value based on the received agent signal values, with the primary agent concentration value determined by giving greater weight to more recent agent signal values. Where the primary agent concentration value exceeds a primary threshold value, an alarm signal may be activated. The processor also may determine a secondary agent concentration value, which may be determined from the actual agent signal values instead of the weighted agent signal values. Where the secondary agent concentration value exceeds a secondary threshold value, an alarm signal may be activated.

Abstract: A process for characterizing a sample comprising a population of linear macromolecules of interest (104) and a population of long chain branched macromolecules of interest (103), the process including four steps. The first step is to provide a flow through separating medium (100) and a liquid eluant (101) in which the macromolecules of interest dissolve, the separating medium defining flow through channels (102), the eluant flow rate and the average diameter of the channels being in a range so that the linear macromolecules of interest elute before the long chain branched macromolecules of interest (105) (106). The second step is to introduce a sample into the liquid eluant. The third step is to flow the liquid eluant under pressure through the channels (102) of the separating medium (100).

Abstract: Products and processes are provided herewith for analyzing octane content in a fuel sample that include the step or steps of receiving an octane measurement of a fuel sample from a octane analyzer, rounding the octane measurement to a nearest recognized octane rating, comparing the rounded octane measurement with a listed octane rating for the fuel sample, and communicating results of the comparison to a user of the octane analyzer. The octane analyzer may be incorporated into a fuel pump or a vehicle. The results of the comparison may also be used to adjust the vehicle operating parameters to account for the actual octane rating of the fuel dispensed into the vehicle.

Abstract: A method and system for detecting, quantifying or characterizing emitting sources. According to an embodiment, an emission source is located by monitoring an area with one or more sensors, determining a plume, generating one or more candidates for the emission source, and using the plume to derive one or more characteristics associated with the emission source, and then locating the emission source based on agreement or convergence of the one or more characteristics.

Abstract: A mass spectrometer comprises an ion detector, an analog-to-digital (A/D) converter, a sample adjuster, and an adder. The A/D converter is configured to receive and sample an analog signal from the ion detector thereby providing a plurality of samples. The adder is configured to sum the samples, and the summed samples define a mass spectrum. The sample adjuster is configured to identify a peak defined by the samples and to suppress at least one of the samples of the peak such that a resolution of a peak within the mass spectrum is enhanced.

Abstract: An improved system and method of analyzing sample data that increases the reliability of peak (compound) detection and identification in the presence of chemical and/or random noise. The sample analysis system includes a compound-separating unit for separating constituent compounds in a sample mixture, a compound-analyzing unit for identifying and quantitating at least one of the separated compounds, and a computer for acquiring data from the compound-separating and compound-analyzing units, for generating a multi-dimensional data set incorporating the acquired data, for executing an algorithm for reducing noise in the data set and for detecting peaks (compounds) in the noise-reduced data set, and for identifying/quantitating the detected compounds.

Abstract: Spectra data collected from a mixture defines an n-dimensional data space (n is the number of data points), and application of PCA techniques yields a subset of m-eigenvectors that effectively describe all variance in that data space. Bach member of a library of known components is examined based by representing each library spectrum as a vector in the m-dimensional space. Target factor testing techniques yield an angle between this vector and the data space. Those library members that have the smallest angles are considered to be potential mixture members and are ranked accordingly. Every combination of the top y library members is considered as a potential solution and a multivariate least-squares solution is calculated using the mixture spectra for each of the potential solutions. A ranking algorithm is then applied and used to select the combination that is most likely the set of pure components in the mixture.

Abstract: Method, system and computer program product for providing real time detection of analyte sensor sensitivity decline is continuous glucose monitoring systems are provided.

Abstract: A method for analyzing a multi-channel chromatogram is realized for accurately resolving overlapping peaks on a multi-channel chromatogram to permit analysis of the composition of a sample. First, components of overlapping peaks are specified. A data matrix Dij is determined, and compressed in the wavelength direction to obtain a data matrix vector Di. Next, the two-dimensional data is deconvoluted, final standard deviation s0 is registered, and the deconvoluted two-dimensional data is reconvoluted to a retention intensity matrix. A quantitative spectral intensity matrix is computed, components are identified, and the identified components are quantified. Subsequently, an eigenvalue problem is solved, and the number n of components is estimated. The deconvolution and computation of the eigenvalue problem are iteratively executed until the peaks are isolated. Then, elution profiles are calculated, the components are identified, and the identified components are quantified.

Abstract: The present invention relates to methods and systems or apparatuses for analyzing fluids. More particularly the present invention relates to apparatuses and methods that employ impedance spectroscopy (IS) for analyzing fuels. Fuels of interest include biofuel, particularly biodiesel. Hand-held and “in-line” IS apparatuses are disclosed.

Abstract: The invention relates to a process for determining a molecular weight distribution in a polymer. When a polymer is prepared, chains of different length are formed. Correspondingly, a distribution of the molecular weights of the chains of a polymer arises. It is an object of the invention to be able to determine the molecular weight distribution in an improved manner compared to the prior art. The object of the invention is achieved by describing starting data G*(?) available in numerical form, i.e. the complex shear modulus measured as a function of frequency or the mastercurve constructed therefrom, are described by an analytical function. In this way, exact knowledge of the relaxation behaviour is available in improved form, in particular also in the case of prolonged relaxation times. This enables a valid determination of the relaxation time spectrum and hence a fundamentally more valid calculation of the molecular weight distribution.

Abstract: A method of screening for disorders of glucose metabolism such as impaired glucose tolerance and diabetes allows prevention, or early detection and treatment of diabetic complications such as cardiovascular disease, retinopathy, and other disorders of the major organs and systems. A mathematical algorithm evaluates the shape of a subject's glucose profile and classifies the profile into one of several predefined clusters, each cluster corresponding either to a normal condition or one of several abnormal conditions. The series of blood glucose values making up the glucose tolerance curve may be measured using any glucose analyzer including: invasive, minimally invasive and noninvasive types. The method is executed on a processing device programmed to perform the steps of the method. Depending on the outcome of the screening, a subject may be provided with additional information concerning their condition and/or counseled to consult further with their health care provider.

Abstract: Systems, methods, and computer programming for collecting data using a mass spectrometer comprising a particle detector or other mass analyzer. A data collection such as a tree or array structure which includes data records for storing detected data is maintained in volatile or persistent memory. Data is received from the mass analyzer. Whether the collection contains data records corresponding to newly-acquired data signals is determined. If the collection does not contain records corresponding to the newly-received records, a new record is added. In either case, the record corresponding to the received data record is updated to reflect reception of the newly-acquired signal.

Abstract: The invention generates mass scale comparability between mass spectra which are acquired in time-of-flight mass spectrometers, particularly with ionization by matrix-assisted laser desorption. Always slightly distorted mass scales of different mass spectra from the same type of sample can be aligned. The flight times of identical ions always differ slightly from one mass spectrum to the next due to non-reproducible processes in the ionization method. Thus the apparent mass values of ion signals of identical substances in different mass spectra do not match even if the flight times are converted into mass values with the identical calibration equation. After alignment of the mass scales, mass spectra can be reliably compared with respect to deviations in intensities of bio-makers, or be added together without deterioration in the mass resolution, and improved reference spectrum libraries can be created. Furthermore, the invention allows more reliable library searches to be carried out.

Abstract: There are many inventions described and illustrated herein. In one aspect, the inventions relate to a system and method to monitor, control, manage and/or measure the delivery of one or more fluids (for example, liquid, gas and/or gas vapor forms of oxygen, nitrogen, carbon dioxide, hydrogen, and/or propane) from a fluid storage unit (whether mobile (for example, portable and/or transportable between a plurality of locations) or immobile (for example, permanently or semi-permanently fixed in a predetermined location)). In another aspect, the present inventions relate to a system and method to fill, refill, distribute, allocate and/or dispense fluid to one or more such fluid storage units (which contain or are capable of containing one or more such fluids).

Abstract: A test device (10) for determining the analyte concentration in a current sample. A measuring unit (28) is included in the test device and is adapted to measure the reaction of a reagent and the analyte and to generate a signal indicative of the measured reaction. The test device (10) also includes a processor (32) that is electronically coupled to the measuring unit (28) and is adapted to determine the analyte concentration in the sample in response to receiving the signal indicative of the measured reaction from the measuring unit (28). Electronically coupled to the processor (32) is a memory (34), the memory (34) for storing the analyte concentration and including storage of a current sample and at least one past sample. The test device (10) further includes a user display (18) that is also electronically coupled to the processor (32), and a display automatically displaying the concentration of the current sample and at least one past sample in a graph.