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This paper proposes a novel approach to the modelling of HTS transformer-rectifier flux pumps that can charge HTS magnet-ic loads without the need for bulky current leads or expensive cryogenic requirements. The model was built in MATLAB/Simulink for a flux pump with 2 HTS switches, an HTS transformer with a primary inductance of 15 mH, second-ary inductance of 50 H and an HTS magnetic load with an in-ductance of 2 mH. With a 5 A pk-pk triangular current wave-form at 2 Hz the system can load the HTS load to 34.63 A in 5 s. This incremental addition of flux to the load demonstrates the advantage of flux pumps as they can charge high-field magnets without the need for large power sources. The speed of flux pumping is improved by increasing the system frequency, the magnitude of the dynamic voltage developed in the HTS switches and by increasing the primary inductance of the trans-former. This has widespread industrial applicability in fields such as the charging of high-field magnets for MRI systems.

Conductor on round core (CORC) cables wound by high-temperature superconducting (HTS) tapes have received much attention due to the advantages in power capacity and mechanical flexibility. This paper first developed a 3D model for a CORC cable through the finite-element method (FEM). Next, the total AC loss caused by transported current only was investigated, revealing the eddy current loss in the tube former contributes to the cable loss. The numerical CORC model was validated by published measurements. Moreover, the AC loss that resulted from a simultaneous presence of transport current and magnetic field was explored. With the induced current, the magnetisation loss generated in superconductors can increase the total loss. It is concluded that the addition of a magnetic field can result in a surge in the total loss of a current-carrying cable.

The conductor on round core (CORC) cable wound with second-generation high-temperature superconducting (HTS) tapes is a promising cable candidate with superiority in current capacity and mechanical strength. The composing superconductors and the former are tightly assembled, resulting in a strong electro-magnetic interaction between them. Correspondingly, the AC loss is influenced by the cable structure. In this paper, a 3D finite-element model of the CORC cable is first built, and it includes the complex geometry, the angular dependence of critical current and the periodic settings. The modelling is verified by the measurements conducted for the transport loss of a two-layer CORC cable. Subsequently, the simulated results show that the primary transport loss shifts from the former to the superconductors as the current increases. Meanwhile, the loss exhibited in the outer layer is larger than that of the inner layer, which is caused by the shielding effect among layers and the former. This also leads to the current inhomogeneity in CORC cables. In contrast with the two-layer case, the simulated single-layer structure indicates stronger frequency dependence because the eddy current loss in the copper former is always dominant without the cancellation of the opposite-wound layers. The core eddy current of the single structure is denser on the outer surface. Finally, the AC transport losses among a straight HTS tape, a two-layer cable and a single-layer cable are compared. The two-layer structure is confirmed to minimise the loss, meaning an even-numbered arrangement makes better use of the cable space and superconducting materials. Having illustrated the electro-magnetic behaviour inside the CORC cable, this work is an essential reference for the structure design of CORC cables.

When a superconductor is exposed to an AC magnetic field whilst carrying a constant DC transport current, a DC electrical resistance can be observed, commonly referred to as “dynamic resistance”. This dissipative effect can play a critical role in many potential high-temperature superconducting (HTS) applications, especially for the AC-field-actuated HTS switch, which is the key component in the HTS transformer-rectifier flux pump (TRFP). The characteristics of the HTS switch determine the performance and reliability of TRFP. In this paper, we report a numerical study of a new HTS switch design made of series-connected YBCO stacks. This study aims to obtain insights into the characteristics of dynamic resistance and power loss, including their relationships with the amplitude and the frequency of the AC magnetic field. The energy conversion efficiency of the HTS switch is also investigated. This work will help design a high-performance AC-field-actuated HTS switch.

Superconducting magnetic levitation train (SC maglev) is developing rapidly in recent decades for its promising features like ultrahigh cruising speed. To develop the second-generation high-temperature superconducting (2G HTS) maglev, serious of works have been done by the group including design of ground propulsive system, optimization of on-board 2G HTS magnet system, energizing test, loss analyses, and over-current duration test. In this work, as one of the most important parts of the development progress, mechanical properties of the on-board 2G HTS magnet system are evaluated, including modal analysis, harmonic response, random vibration, and shock response. Meanwhile, bench tests under much severer mechanical conditions are conducted, resulting in neither mechanical nor electrical damages to the magnet within the tested frequency range. This work is intended to not only raise topics to help design this application concerning long term and safe operation, but also provide with referable method and process for similar mechanical evaluation of other HTS apparatuses used in non-static mechanical environment.

AC loss is an intractable and inevitable issue on high temperature superconducting (HTS) coils. In some HTS devices with the iron core, AC loss in HTS coils have been investigated. However, practically, partial distorted currents can flow in HTS coils, and the AC loss in this situation has rarely been conducted. Here, a normal and distorted current were respectively applied into a double-layer racetrack coil (DRC) to induce AC losses. The numerical and experimental results were obtained with and without laminated silicon steel sheets (LSSS), which showed that the AC loss of the DRC significantly increased when put on the LSSS. Furthermore, compared with the loss generated by the fundamental waveform, currents with 3rd harmonic in phase and 5th out of phase, both with 10% total harmonic distortion (THD) could increase AC loss by 9.3% and 7.8%, respectively. To reduce AC loss of the DRC on the LSSS, two methods are proposed, and it is found that increasing the 5 mm distance vertically and horizontally between the DRC and LSSS could significantly decrease the AC loss by 20.7% and 18.0%, respectively. This study could offer an indispensable reference for designing and operating HTS coils with the iron core for AC applications.

Magnetic switches apply AC magnetic fields to DC current-carrying high temperature superconducting (HTS) tapes to generate DC voltages and are commonly used in the persistent current switches (PCSs) and flux pumps to charge HTS-coated conductor magnets. Normally, they are made of copper field coils and iron cores with narrow air gaps for the HTS tape to pass through. However, the perpendicular components of the self-field of the HTS tape in the air gap can be enhanced by the iron cores and cause a critical current reduction of up to 40% to the tape. If ignored, this reduction, rather than the magnets themselves, will limit the current carrying capability of the HTS magnets. To tackle this problem, we present analytical approximations to calculate the self-field distribution of a superconducting tape between iron cores. The approximate solutions are based on the method of images in electromagnetics to simplify the derivation and are then verified by the experiments and 3D finite element method models using the T–A formulation. The solutions are universal and can be applied to almost all the magnetic switches currently in use. A case study of typical magnetic switches shows that the solutions can be used to determine the critical current reduction quickly and accurately, analyse the influence of different parameters, and simplify the design process of magnetic switches. The results can significantly benefit the design and optimisation of PCSs and flux pumps for HTS magnet charging systems in the future.

This article presents a simplified mathematical model the anisotropic magnetic field dependence (AMFD) for simulating the High-temperature superconducting (HTS) Conductor on Round Core (CORC) Cables. All these simulations of HTS CORC Cable were performed based on the finite-element method (FEM) H -formulation model merged into the numerical platform COMSOL Multi-physics. The simplified model of AMFD was implemented into both the 2D and 3D H -formulation models of HTS CORC cables. Their results were studied with different conditions, such as the increasing transport current, as well as the gap angle between the superconducting tapes in a single layer. This new simplified AMFD model can give a proper approximation of the actual electromagnetic behaviours of the HTS CORC, but also establish the upper limit of the AC loss calculation, which can be fairly useful for designing future HTS CORC cables.

High-temperature superconducting (HTS) tape stacks could be used in motors as a substitute for permanent magnets (PMs) to improve the power density. However, the magnetization difficulty and safety concern limit its wider application. A novel hybrid magnet made of HTS tape stacks and PMs is proposed in this paper and investigated in experimental and numerical modeling methods. A hybrid magnet sample is manufactured and tested using pulsed field magnetization (PFM) at 77.3 K. Then, a 3-D electromagnetic-thermal coupled model is built and verified to simulate the field performance at lower temperatures. After the optimization process of the thickness ratio, an optimal 5-mm hybrid magnet of 0.5-mm tape stack +4.5 mm PM is obtained. Compared with the PM, the optimal hybrid magnet could enhance the magnetic field by 114%. Compared with the pure tape stack of the same size, the hybrid magnet could be magnetized with relatively small pulsed field, could reduce the consumption of the HTS tapes, and could enhance the operation safety especially encountering a cooling system failure. The results offer a novel perspective to introduce the HTS material into the conventional motor applications and provide a possible reference to the future study of HTS motors.

Superconducting magnetic levitation (Maglev) is developing rapidly in recent decades. Compared to traditional railways, superconducting Maglev is superior in aspects such as faster speed, less pollution, and safer operation. The development of second generation (2G) high-temperature superconducting (HTS) wires, which have higher in-field critical current density and mechanical strength, has also improved the design performance of the superconducting Maglev. This paper presents design and optimization processes of no-insulation magnets using 2G HTS wires for a prototype of linear propulsion system in the Maglev. According to the design results, one of the coils in the magnets are manufactured for routine test including IC measurement and Maglev-related tests including field quality comparison, charging characters like delay and loss, over-MMF test and mechanical vibration test simulating the running conditions of the Maglev. The coil has no degradations or obvious changes of performances after the tests. And the test results meet the expected requirements of the prototype.

In this paper, a 30-kW permanent magnet superconducting synchronous generator is proposed for the marine application. The perpendicular magnetic field on the high temperature superconducting (HTS) coils will cause a large drop in critical current and create much more ac loss. The magnetic field consists of two parts, i.e., self-field created by the transport current and external field created by the rotor rotation. It can be reduced by decreasing the distance between the HTS coil and back iron, increasing the distance between the HTS coil and iron teeth or adding the slot wedges in the open slots. These are effective methods to improve HTS armatures’ critical current by reducing the perpendicular magnetic field on the HTS coil surface. Changing the turns ratio of HTS coils has little influence on reducing the maximum perpendicular magnetic field. However, it could decrease the number of flux lines passing through the HTS coil and reduce the total ac loss of the HTS coil.

High-temperature superconducting (HTS) coils could bear larger current density and produce higher magnetic field compared to permanent magnets. An HTS linear synchronous motor (LSM) with its secondary excitation system made of HTS coils can provide larger thrust force but unavoidable larger normal force. This paper focuses on the analysis and comparison of different armature structures in an HTS LSM to improve the magnetic flux waveform quality, decrease the normal force, and simultaneously maintain the thrust force. Five alternative armature structures are proposed and investigated, i.e., coreless double layer lap winding (DLLW), yokeless DLLW, coreless and yokeless DLLW, and flat winding with and without iron yoke. Three dimensional models of HTS LSMs are built and verified to compare the magnetic field and force performances of various armature structures using the finite element method. Results indicate that armatures without iron components perform better. Furthermore, the yokeless flat winding is recommended for its 81% reduction of magnetic flux harmonic component and 52% increase of thrust force compared with DLLW.

Magnetic levitation vehicle (maglev) is a promising candidate for high-speed transportation with features like low pollution and power loss. And the maglev performances are further enhanced by introducing the high-temperature superconducting (HTS) technology to the maglev. In this paper, a 7.55-kW small-scale HTS linear synchronous motor (LSM) is designed as a preparatory research of the propulsion system for the future high-speed maglev. Different from those in a permanent magnet (PM) LSM, the primary and secondary parts are especially designed for an HTS LSM according to the design flow. Performances are analyzed including the comparison between the HTS LSM and the PM LSM. Under the same electromagnetic gap of 10 mm, the maximum propulsive force of the HTS LSM is 1510 N, which is ∼50% larger than that of the PM LSM though the commercial PMs with the strongest remnant field of 1.45 T (N52) are selected and arranged in a Halbach array. And the field waveform of HTS secondary is also more sinusoidal with lower total harmonic distortion. Overall, the HTS LSM performs better than the PM LSM, and the design results can provide possible references for the future high-speed maglev.

For the electrodynamic suspension (EDS) system in the high-speed magnetic levitation (Maglev) train, high-temperature superconducting (HTS) coils made of ReBCO-coated conductors can be used as levitation magnets. In this paper, a three-dimensional (3-D) model of the HTS EDS system is built for the design of the suspension system of a full-scale high-speed Maglev train. Subsequently, the levitation and drag forces are analyzed using finite-element method (FEM), and the force performances of different operating currents, reaction board thicknesses, and air gap lengths are investigated. And the distribution of the eddy current on the reaction board induced by the moving HTS magnets is obtained. Moreover, according to the eddy current distribution and force analysis results, a mirror image method is proposed to simplify the calculation and accelerate the estimation of the saturated levitation force of an HTS EDS system. The calculation results of the model are verified by the FEM model with an error less than 8%. Finally, the model is expanded to a full-scale HTS EDS system, which validates the feasibility of applying to the high-speed Maglev train.

A small-scale linear propulsion system, made of a linear synchronous motor (LSM), is designed for preparatory researches of the future high-speed maglev. The secondary part of the LSM is made of high-temperature superconducting (HTS) no-insulation (NI) magnets. This paper focuses on the design process and performance analysis of the NI HTS magnets. The design target is to optimize the dimensions of the magnets with minimum HTS tapes consumption while generating a qualified magnetic field and operating the magnets safely. Based on the design results, field and critical current distributions in the different locations of the magnets are investigated to provide references for critical current determination. The magnets are designed to operate at temperature of 30 K with a magneto-motive force of ∼295 kA and stored energy of ∼25 kJ. The average fundamental component of the field at 70 mm beneath the bottom of the magnets is 0.53 T (RMS), and the charging time of the magnets is ∼41 min, with maximum charging loss of 16 W. The design results meet the requirement of the LSM.

Introduction of superconductor to magnetic levitation (maglev) trains greatly enhances the performances compared to those of normal conductor maglevs, e.g. from 430 km/h of the Transrapid (in Shanghai) to 603 km/h of the L0 Series in Japan. However, one of the important constraints on development of superconducting maglevs is limited wireless feeding power for on-board superconducting magnets and cryogenic cooling. In this paper, a persistent-current superconducting magnets system with solid nitrogen (SN2) cooling preservation is proposed for liberation of its demanding on-board power feeding requirement. The magnets are optimally designed with no-insulation technique guaranteeing a safe operation with magnetic field over 0.8 T. Lasting time of persistent current (at 96.5% magnetic field retained) and SN2 cooling preservation (up to 40 K) is all >9 h, covering a maglev traveling distance of >5400 km at average designed speed of >600 km/h. The magnets have anti-vibration ability of 15 g (147 m/s2) up to 350 Hz, which has covered the vibratory motion range in maglevs. This work is intended to provide a reference for superconducting maglev developments.

This work relates to improvement of magnetic and cryogenic energy preservation performances in an on-board high-temperature superconducting magnet system used in linear synchronous motors for ultrahigh speed maglevs. Since maglevs remove all the physical contacts to the ground, the wireless on-board feeding power is rather limited especially for superconducting subassemblies. And it has become one of the development bottlenecks. For the magnet system, realization of on-board feeding-power free is pivotal, which is regarding to two important energy conversions: electrical to magnetic energy by persistent-current mode of superconductivity, and latent heat to effective cooling (or cryogenic) energy by α-β phase transition of solid nitrogen (SN2) in the system. Improvements of the two energy conversions are the main work. Firstly, model and numerical approach of persistent-current mode are proposed, followed by simulation of SN2 cooling. Then performances of persistent-current mode and cryogenic energy preservation are reported. Energy conversion efficiency is also analyzed for a strategy to improve cooling performance. The strategy successfully extends cryogenic energy preservation time to 8.83 h and suppresses thermal non-uniformity to

High temperature superconducting (HTS) coils can produce stronger magnetic fields compared with conventional permanent magnet. Superconducting magnets wound by YBCO coated conductors can be used on high-speed maglev train, wind generator, energy storage, and other applications. In some cases, such as the rotor of the long-stator linear synchronous motor, superconducting magnets carry a DC current under an external AC magnetic field, because of the harmonics of the stator current and the rotor vibration. The AC loss generated by the external AC field is an essential issue for selecting the capacity of the refrigerator. In this paper, a numerical model of a large-scale circular superconducting magnet is built in order to study its AC losses under the external AC magnetic field. Then the AC losses of the DC HTS magnet under external AC field with different amplitudes and frequencies are calculated, and according to the calculation, the change rules of AC loss versus the amplitude and frequency of the magnetic field are obtained.

High speed transportations gradually become promising and important in economic development of a country. Maglev, as one of the novel high speed transportations, has been operated commercially like Shanghai Maglev Trains. To enable even faster speed, superconducting Maglev is proposed with the slider in its linear synchronous motor (LSM) is made of high-temperature superconducting (HTS) magnets. The HTS magnets can provide rather strong magnetic field intensity to not only ensure large thrust during operation but also reduce copper consumed in the LSM stator. This paper presents a conceptual design of a HTS magnet used as the slider in a small-scale LSM which is tested for future high-speed superconducting Maglev application. Purpose of the design is to find optimal dimensions of the magnet to reduce HTS tape consuming while meeting the spatial constraints and generating a required magnetic field intensity. Results of the design parameters are plausible. Furthermore, the weakest points corresponding to the lowest critical current in the winding pack are also investigated according the designed parameters, for the sake of operation safety of the HTS magnet.

The Database of Genotypes and Phenotypes (dbGap, http://www.ncbi.nlm.nih.gov/gap) is a National Institutes of Health-sponsored repository charged to archive, curate and distribute information produced by studies investigating the interaction of genotype and phenotype. Information in dbGaP is organized as a hierarchical structure and includes the accessioned objects, phenotypes (as variables and datasets), various molecular assay data (SNP and Expression Array data, Sequence and Epigenomic marks), analyses and documents. Publicly accessible metadata about submitted studies, summary level data, and documents related to studies can be accessed freely on the dbGaP website. Individual-level data are accessible via Controlled Access application to scientists across the globe.

The National Center for Biotechnology Information has created the dbGaP public repository for individual-level phenotype, exposure, genotype and sequence data and the associations between them. dbGaP assigns stable, unique identifiers to studies and subsets of information from those studies, including documents, individual phenotypic variables, tables of trait data, sets of genotype data, computed phenotype-genotype associations, and groups of study subjects who have given similar consents for use of their data.

The conserved domain database (CDD) is part of NCBI's Entrez database system and serves as a primary resource for the annotation of conserved domain footprints on protein sequences in Entrez. Entrez's global query interface can be accessed at http://www.ncbi.nlm.nih.gov/Entrez and will search CDD and many other databases. Domain annotation for proteins in Entrez has been pre-computed and is readily available in the form of 'Conserved Domain' links. Novel protein sequences can be scanned against CDD using the CD-Search service; this service searches databases of CDD-derived profile models with protein sequence queries using BLAST heuristics, at http://www.ncbi.nlm.nih.gov/Structure/cdd/wrpsb.cgi. Protein query sequences submitted to NCBI's protein BLAST search service are scanned for conserved domain signatures by default. The CDD collection contains models imported from Pfam, SMART and COG, as well as domain models curated at NCBI. NCBI curated models are organized into hierarchies of domains related by common descent. Here we report on the status of the curation effort and present a novel helper application, CDTree, which enables users of the CDD resource to examine curated hierarchies. More importantly, CDD and CDTree used in concert, serve as a powerful tool in protein classification, as they allow users to analyze protein sequences in the context of domain family hierarchies.

A human cDNA was isolated encoding a protein with significant sequence similarity (41% identity) to the BVP RNA 5'-phosphatase from the Autographa californica nuclear polyhedrosis virus. This protein is a member of the protein-tyrosine phosphatase (PTP) superfamily and is identical to PIR1, shown by Yuan et al. (Yuan, Y., Da-Ming, L., and Sun, H. (1998) J. Biol. Chem. 272, 20347-20353) to be a nuclear protein that can associate with RNA or ribonucleoprotein complexes. We demonstrate that PIR1 removes two phosphates from the 5'-triphosphate end of RNA, but not from mononucleotide triphosphates. The specific activity of PIR1 with RNA is several orders of magnitude greater than that with the best protein substrates examined, suggesting that RNA is its physiological substrate. A 120-amino acid segment C-terminal to the PTP domain is not required for RNA phosphatase activity. We propose that PIR1 and its closest homologs, which include the metazoan mRNA capping enzymes, constitute a subgroup of the PTP family that use RNA as a substrate.

Human T cell protein tyrosine phosphatase (TCPTP) is a nontransmembrane enzyme, the first of the protein tyrosine phosphatase family to be cloned. Alternative mRNA splicing results in variation in the sequence at the extreme C terminus of TCPTP and generates a 45-kDa form (TC45) that is targeted to the nucleus and a 48-kDa variant (TC48) associated with membranes of the endoplasmic reticulum. In this report, we assessed the role of the C-terminal, noncatalytic segment of TCPTP in regulating activity, concentrating primarily on the TC45 variant. We have demonstrated that limited tryptic proteolysis of TC45 releases first a 42-kDa fragment, then a 33-kDa catalytic domain. Using reduced carboxyamidomethylated and maleylated lysozyme as substrate (RCML), the catalytic domain displays 20-100-fold more activity than the full-length enzyme. Analysis of the time course of limited trypsinolysis revealed that proteolytic activation occurred following cleavage of a protease-sensitive region (residues 353-387) located at the C terminus of TC45. The activity of truncation mutants illustrated that removal of 20 C-terminal residues was sufficient to activate the enzyme fully. The 33-kDa catalytic domain, but not the full-length enzyme, was inhibited in a concentration-dependent manner by addition of the noncatalytic C-terminal segment of TC45. A monoclonal antibody to TCPTP, CF4, which recognizes an epitope located between residues 350 and 363, was capable of fully activating TC45. These data indicate that the noncatalytic segment of TC45 contains an autoregulatory site that modulates activity via a reversible intramolecular interaction with the catalytic domain. These studies suggest that the C-terminal noncatalytic segment of TC45, and possibly TC48, may not only direct the enzyme to different subcellular locations but may also modulate activity in response to the binding of regulatory proteins and/or posttranslational modification.

Proteoliposomal vesicles reconstituted with sarcoplasmic reticulum ATPase and exogenous lipids sustain ATP-dependent Ca2+ uptake and H+ ejection, as well as net charge displacement by Ca2+. We have studied the effect of lumenal (inner) and medium (extravesicular) pH variations on the countertransport ratios of H+ and Ca2+. We find that the Ca2+/H+ molar ratio is approximately 1 when the lumenal and medium pH is near neutrality, but changes with a specific pattern when the medium pH is varied in the presence of a constant lumenal pH and when the lumenal pH is varied in the presence of a constant medium pH. Empirical analysis of the experimental data shows that the apparent pK of the residue(s) releasing H+ into the medium is approximately 6.1, whereas the apparent pK of the residue(s) binding lumenal H+ is approximately 7.7. Assuming that the same acidic residues are involved in H+ and Ca2+ countertransport, our findings suggest a lower affinity for H+ in their outward orientation (prevalent in the ground state of the enzyme) and a higher affinity for H+ in lumenal orientation (prevalent in the phosphorylated state of the enzyme). Cyclic pK changes, coupled to ATP utilization, promote cation exchange, Ca2+ uptake, and H+ ejection by the vesicles. The stoichiometry of countertransport and net charge displacement is matched by a corresponding electrogenic behavior. A calculation of voltage development related to initial rates of charge transfer (dV/dt = (dQ/dt)/Cm) is given as a corrective replacement of a previous steady state calculation.

A reconstituted proteoliposomal system was obtained with Ca-ATPase purified from human erythrocyte membrane (plasma membrane, PM ATPase), and liposomes prepared by reverse-phase evaporation. The reconstituted PM ATPase behaved as an electrogenic Ca2+/H+ exchanger and, under optimal conditions, utilization of 1 mol of ATP was accompanied by uptake of one Ca2+ by the vesicles, and ejection of one H+ from the lumen of the vesicles. Ca2+ uptake was greatly (5-fold) stimulated by the addition of calmodulin, and by collapsing the H+ gradient with the ionophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone. In the presence of calmodulin and p-trifluoromethoxyphenylhydrazone, the reconstituted system sustained transport rates of 1.00 +/- 0.12 mumol of Ca2+/mg of protein min-1 (30 degrees C), reaching asymptotic levels of 8.05 +/- 0.41 mumol of Ca2+/mg of protein (i.e. 20 mM lumenal Ca2+). The corresponding net charge transfer produced a maximal electrical gradient of 40.5 +/- 1.8 mV at steady state. Demonstration of the electrogenic behavior of the PM ATPase, obtained for the first time with these experiments, was critically dependent on the detergent used in the reconstitution procedure. The lumenal pH rise had a much greater rate-limiting effect on the pump, than the electrical potential developed by the pump.

The rad17 gene of Schizosaccharomyces pombe plays an important role as a checkpoint protein following DNA damage and during DNA replication. The human homologue of S. pombe rad17, Hrad17, was recently identified, but its function has not yet been established. Using the yeast two-hybrid system, we determined that HRad17 can interact with a nucleolar protein, NHP2L1. This interaction was also demonstrated biochemically, in human cells. Immunofluorescence studies revealed that HRad17 and NHP2L1 colocalize to the nucleolus, and immunogold labeling further resolved the location of NHP2L1 to the dense fibrillar component of the nucleolus. Interestingly, the localization of HRad17 in the nucleolus was altered in response to UV irradiation. These results provide some insight into the DNA damage and replication checkpoint mechanisms of HRad17.