Browsing by Author "Nithya C"

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2,3′˗DIAMINO˗4,4′˗STILBENEDICARBOXYLIC ACID SENSITIZER FOR DYE SENSITIZED SOLAR CELLS: QUANTUM CHEMICAL INVESTIGATIONS
(Springer Berlin Heidelberg, 2013-10-01) Senthilkumar P; Nithya C; Anbarasan P M
The metal-free organic dye sensitizer 2,3′-diamino-4,4′-stilbenedicarboxylic acid has been investigated for the first time for dye-sensitized solar cell applications. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations (performed using the hybrid functional B3LYP) were carried out to analyze the geometry, electronic structure, polarizability, and hyperpolarizability of 2,3′-diamino-4,4′-stilbenedicarboxylic acid used as a dye sensitizer. A TiO2 cluster was used as a model semiconductor when attempting to determine the conversion efficiency of the selected dye sensitizer. Our TD-DFT calculations demonstrated that the twenty lowest-energy excited states of 2,3′-diamino-4,4′-stilbenedicarboxylic acid are due to photoinduced electron-transfer processes. Moreover, interfacial electron transfer between a TiO2 semiconductor electrode and the dye sensitizer occurs through electron injection from the excited dye to the semiconductor’s conduction band. Results reveal that metal-free 2,3′-diamino-4,4′-stilbenedicarboxylic acid is a simple and efficient sensitizer for dye-sensitized solar cell applications.
BI2O3@REDUCED GRAPHENE OXIDE NANOCOMPOSITE: AN ANODE MATERIAL FOR SODIUM-ION STORAGE
(WILEY‐VCH Verlag, 2015-05-27) Nithya C
The high capacity, excellent cyclability, and good rate capability of reduced graphene oxide (rGO) anchored with Bi2O3 nanocomposite for sodium‐ion batteries is reported. A simple reduction method is adapted to deposit spherical Bi2O3 nanoparticles on the surface of rGO sheets. The surfactant cetyltrimethylammonium bromide (CTAB) plays a major role in controlling the morphology of the Bi2O3 nanoparticles. This Bi2O3@rGO nanocomposite has the advantages of high reversible capacity with a capacity retention (at high rate) of 70.2 % after 200 cycles at a current density of 350 mA g−1. This superior performance can be attributed to the fact that rGO sheets hamper the volume expansion of Bi2O3 nanoparticles and result in faster diffusion of Na+ ions (diffusion coefficient: 5.12×10−8 cm2 s−1) and smaller internal resistance (84.17 Ω) compared with pristine Bi2O3 nanoparticles. The results suggest that anchoring rGO sheets with metal oxides is one of the simplest ways to enhance the electrochemical performance of sodium‐ion batteries.
CARBON PAPER AS A PROMISING FREE STANDING ANODE FOR SODIUM ION BATTERIES
(IOP Publishing Ltd, 2020-12-21) Sadiya Waseem; Nithya C; Priyanka H Maheshwari; Dhakate S R
Porous conducting carbon fiber composite papers have been developed by a two-step process. This involves fabrication of carbon fiber preform followed by composite formation. Different composite papers have been developed by varying the final heat treatment temperature of the composite, viz. 800 °C, 1100 °C, 1400 °C, 1800 °C and 2300 °C. The study gives an insight as to how the structure, porosity, morphology, electrical and mechanical properties of the carbon/carbon composites vary with temperature; and further the effect of these variations on the performance of the composites as anode material for Na-ion batteries. The sample heat-treated to 800 °C showed high reversible capacity of 278 mAh g−1 at a current density of 37 mA g−1. Additionally, high columbic efficiency (>99%) and 72% retention of the initial capacity has been demonstrated for 1000 cycles. This exceptional performance is attributed to the small crystallite size, large d-spacing and disordered structure of the sample which favors the insertion/de-insertion of sodium ion into the composite anode. Hence, it seems as a promising anode material for sodium-ion batteries.
CHAPTER FIFTEEN - NANOSTRUCTURED TRANSITION METAL CHALCOGENIDES FOR RECHARGEABLE BATTERIES
(Elsevier, 2021-01-29) Nithya C; Gopukumar S
Rechargeable lithium/sodium-ion batteries and emerging potassium-ion batteries are considered as the promising energy storage devices for potential high-current rate applications. It has been considered that transition metal chalcogenides (mono- and di-) are a class of two-dimensional compounds (metal sulfides and metal selenides) attracting growing research interest as an anode materials for rechargeable batteries. They have shown efficient energy storage properties owing to their unique physiochemical properties. In this chapter, we systematically discussed and summarized the recent research progress on the nanostructured transition metal chalcogenides (TMCs) for LIBs, NIBs, and KIBs. Here, we presented the electrochemical reaction kinetics, challenging issues, and effective strategies toward the improvement of TMCs for rechargeable batteries. To the end the remaining challenges and outlooks for the further development of TMCs in the field of rechargeable batteries are proposed.
DEVELOPMENT OF FREE STANDING ANODES OF HIGH ASPECT RATIO CARBON MATERIALS FOR RECHARGEABLE LI-ION BATTERIES
(Elsevier, 2013-01-03) Maheswari P H; Nithya C; Shilpa Jain; Mathur R B
Carbon materials of various types have been extensively used as negative electrode materials for rechargeable Li-ion batteries because of their consistent performance and potentialities. High aspect ratio (>1000) carbons such as carbon fibers and multiwalled carbon nanotubes (MWCNTs) of different dimensions have been employed to fabricate free standing anode materials. Various characterization techniques such as SEM, TEM, TGA, XRD, Raman spectroscopy, mercury intrusion porosimetry has been carried out to evaluate the structure of the anode that was further correlated to its performance in Li-ion cell. MWCNTs prepared under specified conditions not only exhibits high purity and crystallinity in structure but also shows exceptional electrochemical behavior of increasing capacity with successive cycling. This is probably due to the formation of a very constructive SEI with negligible charge transfer resistance as shown by the Nyquist plots.
DIAMONDOID-STRUCTURED CU–DICARBOXYLATE-BASED METAL–ORGANIC FRAMEWORKS AS HIGH-CAPACITY ANODES FOR LITHIUM-ION STORAGE
(WILEY‐VCH Verlag, 2014-11-10) Senthikumar R; Nithya C; Gopukumar S; AnbuKulandainathan M
A versatile electrochemical synthetic route is proposed for the preparation of [Cu2(C8H4O4)4]n metal–organic frameworks. The synthesized composites are characterized by using XRD, SEM, FTIR, and Brunauer–Emmett–Teller (BET) surface analysis. The average particle size was measured to be 8.27 nm and the pore size determined to be 14.06 nm. Here, for the first time, we demonstrate the Cu‐based metal–organic frameworks [Cu2(C8H4O4)4]n as a new class of porous crystalline materials that have the ability to reversibly store Li+ ions. Galvanostatic charge/discharge studies suggest that the terephthalate network reversibly reacts with Li and shows high capacity retention (≈84 % over 50 cycles). The best reversible capacity of 227 mAh g−1 (approximately 95 % of the theoretical capacity) has been achieved in the first cycle at a current density of 24 mA g−1. An easily scalable electrochemical synthesis of the [Cu2(C8H4O4)4]n metal–organic frameworks is an attractive candidate for use with lithium‐ion batteries.
EFFECT OF DONOR (TETRADECYLOXY) AND ACCEPTOR (CARBOXAMIDE) GROUPS IN TRANS-STILBENE FOR DSSCS: QUANTUM CHEMICAL INVESTIGATIONS
(Elsevier, 2014-01-03) Senthilkumar P; Nithya C; Anbarasan P M
Incorporation of tetradecyloxy and carboxamide groups in trans-stilbene molecule (dye) has been investigated first time for Dye Sensitized Solar Cells (DSSCs) applications. To understand the changes in electronic structure, geometry, dipole moment and polarizability of the mentioned dye architecture has been carried out by using density functional theory (DFT) and time dependent DFT calculations using hybrid functional B3LYP method. Further, the semiconductor TiO2 is also used as a model to evaluate the photo conversion efficiency of the chosen dye architecture. Results reveal that tetradecyloxy and carboxamide groups act as an excellent donor and acceptor groups respectively which give rise to larger difference in excited state dipole moment than the ground state. This kind of stilbene based metal free organic dyes are act as a promising sensitizer for practical DSSCs applications.
EFFECT OF MG DOPANT ON THE ELECTROCHEMICAL PERFORMANCE OF LINI0.5MN0.5O2 CATHODE MATERIALS FOR LITHIUM RECHARGEABLE BATTERIES
(IOP Publishing, 2010-06-16) Nithya C; Lakshmi R; Gopukumar S
Positive electrode materials, LiMg x Ni0.5−x Co0.5O2 (x = 0 < x < 0.5), have been successfully synthesized by microwave-assisted solution technique. The precursor has been analyzed by TG/DTA and the powder was calcined at 850 °C. The XRD patterns reveal that the synthesized materials exhibit hexagonal layered structure corresponding to R3-m space group. Coin cells of 2016 type have been fabricated using the synthesized layered material as cathode active material and lithium foil used as counter and reference electrode. Test cells were operated in the potential limits between 2.7 and 4.3 V using 1 M LiPF6 in 1:1 EC/DEC as electrolyte. LiMg0.2Ni0.3Co0.5O2 material delivers an average discharge capacity of around 165 mA hg−1 at 0.1 C rate over the investigated 20 cycles.
EFFECT OF MG DOPING ON THE LOCAL STRUCTURE OF LIMGYCO1−YO2 CATHODE MATERIAL INVESTIGATED BY X-RAY ABSORPTION SPECTROSCOPY
(Elsevier, 2014-04-15) Cheng H; Pan C J; Nithya C; Thirunakaran R; Gopukumar S; Chen C H; Lee J F; Chen J M; Sivashanmugam A; Hwang B J
A higher capacity and better cyclability are apparent when magnesium is introduced into the structure of LiCoO2 (y = 0.15). XRD analysis of LiMgyCo1−yO2 (y = 0, 0.1, 0.15), synthesized at 800 °C using a microwave assisted method, shows that the material is in the R-3m space group and to have a slightly expanded unit cell that increases with greater magnesium doping. Structural analysis by X-ray absorption spectroscopy (XAS) at the Co K-edge, L-edge and O K-edge shows that the magnesium is located in the transition metal layer rather than in the lithium layer and the charge balance results from the formation of oxygen vacancies rather than Co4+, while cobalt remains in the 3+ oxidation state. Interestingly, oxygen is found to participate in the charge compensation. Both magnesium, in the transition metal layer, and the Co-defect structure are attributed to the contribution towards structural stabilization of LiCoO2, thereby resulting in its enhanced electrochemical performance.
ELECTROCHEMICAL BEHAVIOUR OF MG67NI(33-X)NBX (X= 0,1,2 AND 4) ALLOY SYNTHESIZED BY HIGH ENERGY BALL MILLING
(Elsevier, 2014-01-01) Venkateswari A; Nithya C; Kumaran S
The effect of Niobium (Nb) on charge-discharge behaviour of Mg67Ni(33-x)Nbx (x= 0, 1, 2 and 4) alloys synthesized by high energy ball milling was examined using electrochemical method. Mg67Ni33 alloys with varying Nb concentration has been synthesized and characterized by various characterization techniques viz., XRD and SEM (EDS) etc. XRD pattern of the synthesized alloys reveal the formation of Mg2Ni intermetallic with NbO2 oxide on the surface of Mg2Ni compound, which prevents the corrosive nature of electrode material. However, the stable oxide film formed on the surface of Mg2Ni compound decreases the electrochemical properties of the electrode i.e., diffusion of hydrogen and discharge capacity which is due to the passivation nature of the oxide film.
ELECTROCHEMICAL STUDIES ON CRYSTALLINE CUS AS AN ELECTRODE MATERIAL FOR NON-AQUEOUS NA-ION CAPACITORS
(Royal Society of Chemistry, 2020-03-03) Goswami M; Nithya C; Sathish N; Satendra Kumar; Singh N; Srivastava A.K; Surender Kumar
CuO and its gallium composites with various compositions are successfully fabricated Current investigations are concentrated on the development of high-performance electrode materials for sodium-ion capacitors (NICs). Copper sulphide can be employed as an electrode material for sodium-ion capacitors owing to its electrical conductivity and specific capacity. Crystalline CuS provides a large surface area for Na insertion/extraction. In this context, we have reported CuS powder synthesised via a simple wet chemical route. XRD and FT-IR studies have been carried out to determine the phase formation and confirm the purity of the CuS powder. A specific surface area of 62 m2 g−1 is measured by a BET surface area analyser. NICs were assembled in a non-aqueous medium with CuS particles and investigated for charge–discharge cycling in the potential window from 0.01 to 3 V. Cyclic voltammetry (CV) confirmed that at a high scan rate from 10 mV s−1 to 100 mV s−1, the CuS particles showed ideal capacitive behaviour. The calculated value of specific capacitance was 160 F g−1 for the CuS particles. At a scan rate of 1 mV s−1, 74.8% capacitive contribution was obtained from the CuS particles. Electrochemical impedance spectroscopy (EIS) revealed the interfacial interactions of the CuS particles with an Na-based electrolyte.
EXPERIMENTAL INVESTIGATION AND MECHANISM OF CRITICAL HEAT FLUX ENHANCEMENT IN POOL BOILING HEAT TRANSFER WITH NANOFLUIDS
(Springer Berlin Heidelberg, 2016-11-01) Kamatchi R; Venkatachalapathy S; Nithya C
In the present study, reduced graphene oxide (rGO) is synthesized from graphite using modified Hummer and chemical reduction methods. Various characterizations techniques are carried out to study the in-plane crystallite size, number of layers, presence of functional groups and surface morphology. Different concentrations of 0.01, 0.1, and 0.3 g/l of rGO/water nanofluids are prepared by dispersing the flakes in DI water. The colloidal stability of 0.3 g/l concentration is measured after 5 days using Zetasizer and found to be stable. The rGO/water nanofluids are then used to study the effect on the enhancement of critical heat flux (CHF) in pool boiling heat transfer. Results indicate an enhancement in CHF ranging from 145 to 245 % for the tested concentrations. The mechanisms of CHF enhancement are analyzed based on surface wettability, surface roughness, and porous layer thickness. The macrolayerdryout model sufficiently supports the mechanism of CHF enhancement of thin wire with rGO deposits, which is not reported yet.
EXPLORATION OF V2O5NANOROD@RGOHETEROSTRUCTURE AS POTENTIAL CATHODE MATERIAL FOR POTASSIUM-ION BATTERIES
(Elsevier, 2019-06-20) Vishnuprakash P; Nithya C; Premalatha M
Potassium-ion batteries (KIBs) are considered as an alternative energy storage device for lithium-ion batteries (LIBs) owing to the low cost and earth abundant. Herein, first time we report the hydrothermally synthesized Bacilli rod shape V2O5 and making composite with reduced graphene oxide (rGO) for KIBs which greatly boosting the cycle durability and rate capability. Sheet-like materials (rGO) greatly enhance the performance of energy storage materials due to their high surface area which largely improves the electrochemical reaction kinetics. The heterostructure of V2O5 nanorods anchored on highly conductive rGO matrix not only enhance the reaction kinetics but also offer a more reactive surface area for potassium-ion storage resulting superior cycling stability. The V2O5@rGO exhibits a reversible capacity of 271 mAhg−1 and retains 80% initial discharge capacity after 500 cycles. It shows excellent rate capability and delivers 50 mAhg−1 even at the high current density of 2940 mAg−1 (10C). Ex-situ TEM and XRD analysis confirmed that the rod-shape with sheet like rGO morphology is retained after 500 cycles. The design of nanorod@sheet like architecture becomes a promising cathode candidate for high performance KIBs
HETEROSTRUCTURE OF TWO DIFFERENT 2D MATERIALS BASED ON MOS2NANOFLOWERS@RGO: AN ELECTRODE MATERIAL FOR SODIUM-ION CAPACITORS
(Royal Society of Chemistry, 2018-09-05) Kiruthiga R; Nithya C; Karvembu R
Sodium ion capacitors are under extensive investigation as companionable pre-existing lithium ion batteries and sodium ion batteries. Finding a suitable host for sodium ion storage is still a major challenge. In this context, here we report a MoS2 nanoflowers@rGO composite produced via a hydrothermal method followed by an ultra sonication process as a sodium ion symmetric hybrid supercapacitor. The structural and electrochemical performances of the electrode material were investigated to establish its applicability in sodium ion capacitors. The electrochemical performance was evaluated using metallic sodium in a half cell configuration which delivered a maximum specific capacitance of 226 F g−1 at 0.03 A g−1. When examined as a symmetric hybrid electrode (full cell) it delivered a maximum capacitance of 55 F g−1 at 0.03 A g−1. This combination may be a new gateway for upcoming research work which deals with sodium ion storage applications. The results confirmed that the as-synthesized MoS2 nanoflowers@rGOheterostructure electrode exhibited notable electrochemical behaviour.
HIGH PERFORMANCE NAXCOO2 AS A CATHODE MATERIAL FOR RECHARGEABLE SODIUM BATTERIES
(Royal society of Chemistry, 2015-07-24) Venkata Rami Reddy B; Ravikumar R; Nithya C; Gopukumar S
Sodium cobalt oxide (NCO) has been synthesized by a glycine assisted sol–gel combustion method. XRD studies confirm the P2 phase formation of NCO. Na exists in two different environments in the NCO crystallite structure, which is confirmed by 23Na Nuclear Magnetic Resonance spectra (NMR). Morphological studies confirm that the particles are unique with a stacked hexagonal shape. Galvanostatic charge/discharge studies performed at different current rates (0.1, 0.2 and 0.5) deliver reversible specific capacities of 126, 108 and 77 mA h g−1 respectively. Further, cycle life performance of the fabricated cells after 50 cycles at 0.1 C rate exhibits an average discharge capacity of ~121 mA h g−1 with a capacity retention of ~86% (Coulombic efficiency ~99.9%). The investigated NCO's superior performance suggests its suitability as a cathode material for Na-ion batteries.
HIGH PERFORMANCE SODIUM ION CAPACITOR BASED ON GOAT HAIR DERIVED CARBON AND MOO2@RGO NANO COMPOSITE ELECTRODES
(American Chemical Society, 2018-02-26) Kiruthiga R; Nithya C; Karvembu R
Sodium ion based energy storage system is a rising alternative for imminent energy need. Especially sodium ion hybrid supercapacitors have attracted much attention because they store energy through battery-type anode and offer power by capacitor-type cathode. Accomplishing high energy and power densities in a single device is of significant interest, which can probably be done merely by making hybrid devices. Herein we have synthesized biomass (goat hair) derived activated carbon cathode with a high surface area of 2042 m2g–1 and MoO2@rGO composite anode materials. Goat hair, keratin rich biomass, has a great impact economically, and over 40 million tons per year is produced. Besides, reduced graphene oxide (rGO) has been used to facilitate the chemical stability, mechanical strength, and feasible pathway for electrochemical reactions of MoO2. Each electrode individually (half-cell) and combinedly (full-cell) showed good electrochemical performance which is almost equal to previously reported sodium ion based hybrid supercapacitors. This combination of supercapacitor can travel over the existing energy storage system to the next level
HIGH PERFORMING SNXSBYCUZ COMPOSITE ANODES FOR LITHIUM ION BATTERIES
(Elsevier Masson, 2013-05-01) Nithya C; Sowmiya T; VijayaBaskar K; Selvaganeshan N; Kalaiyarasi T; Gopukumar S
To increase the volumetric discharge capacity of negative electrode for rechargeable lithium batteries, a composite anode SnxSbyCuz has been synthesized by using high energy mechanical ball milling method. The synthesized composite anode materials have been characterized by X-ray diffraction and SEM analysis. The charge/discharge characteristics of the fabricated coin cells have been evaluated galvanostatically in the potential range 0.01–2 V using 1 M LiPF6 in 1:1 EC/DEC as electrolyte. Results indicate that the composition with 90 wt% Sn, 8 wt% Sb and 2 wt% Cu delivers an average discharge capacity of 740 mAh g−1 over the investigated 50 cycles which is a potential candidate for use as an anode material for lithium rechargeable cells.
HIGH-CAPACITY SOL−GEL SYNTHESIS OF LINIXCOYMN1−X−YO2 (0 ≤ X, Y ≤ 0.5) CATHODE MATERIAL FOR USE IN LITHIUM RECHARGEABLE BATTERIES
(American Chemical Society, 2009-10-15) Nithya C; Thirunakaran R; Sivashanmugam A; Kiruthika G V M; Gopukumar S
Succinic acid assisted sol−gel synthesized layered LiNixCoyMn1−x−yO2 (0 ≤ x, y ≤ 0.5) materials have been studied as cathode materials for lithium rechargeable batteries. TG/DTA studies were performed on the gel precursor and suggest the formation of a layered phase around 400 °C. The gel precursor was calcined at 850 °C and characterized by means of X-ray diffraction and FT-IR analyses and reveals that all of the synthesized materials are found to be well-crystallized with an α-NaFeO2 layered structure. The effect of Co content on the surface morphology has been examined by scanning electron microscopy, and X-ray photoelectron spectroscopy studies indicate that the oxidation states of nickel, cobalt, and manganese are +2, +3, and +4, respectively. The electrochemical galvanostatic charge/discharge cycling behavior of the synthesized layered materials has been evaluated in the voltage range of 2.7–4.8 V at C/10 and C/5 rates. LiCo0.1Ni0.4Mn0.5O2 cathode material delivered the highest average discharge capacity of ~175 mAh/g at C/10 rate over the investigated 50 cycles.
HYDROTHERMAL FABRICATION OF MNCO3@RGO: A PROMISING ANODE MATERIAL FOR POTASSIUM-ION BATTERIES
(Elsevier, 2019-08-01) Nithya C; Lee J H; Kim N H
A simple one-step hydrothermal method is used for the fabrication of MnCO3 nanorods@rGO composite without any further heat treatment. MnCO3 nanorods with size of ~5–10 nm in diameter are anchored well on the surface of rGO sheets. The sheet-like nature of rGO is well maintained in the composites. The MnCO3 nanorods@rGO composite provides high surface area (122.6 m2 g−1) for conversion reaction and delivers high capacity and superior long-term cycling performance for potassium-ion batteries. The composite delivers a high capacity of 841 mAhg−1 and retains 88% capacity at the current density of 200 mAg−1 after 500 cycles. Even at the high current density of 2000 mAg−1, the material still delivers a stable capacity 98 mAhg−1 and maintains over in subsequent cycles. From the ex-situ TEM analysis, we confirmed that the morphology and structure of the composite is preserved after 500 cycles. This further confirms that rod-like morphology on rGO sheets acts as a stable template for reversible potassium intercalation/deintercalation. Moreover, rGO sheets accommodate the volume expansion during cycling and provide structural stability for MnCO3 nanorods
INFLUENCE OF GA2O3, CUGA2O4 AND CU4O3 PHASES ON THE SODIUM-ION STORAGE BEHAVIOUR OF CUO AND ITS GALLIUM COMPOSITES
(Royal Society of Chemistry, 2020-02-14) Rekha P; Nithya C; Gopala Krishnan N
CuO and its gallium composites with various compositions are successfully fabricated by using a hydrothermal technique followed by calcination at 900 °C. The added Ga precursors formed oxides in the composites, such as Ga2O3, CuGa2O4 and Cu4O3, as confirmed through the X-ray diffraction patterns as well as the HRTEM and SAED patterns. Further HRTEM analysis also confirmed that Cu4O3 and CuGa2O4 phases reside on the surface of CuO in the composites with a CuO : Ga ratio of 90 : 10. The contents of various oxide phases varied when we increased the amount of Ga in the CuO composites. Changing the ratios of CuO and Ga precursors in the composites is quite effective in tailoring the sodium-ion storage behaviour of CuO. The resultant CuO/Ga composites exhibit remarkable electrochemical performance for sodium-ion batteries in terms of capacity, rate capability and cycling performance. The composite containing 90% CuO and 10% Cu/Ga oxides delivers the highest charge capacity of 661 mA h g−1 at a current density of 0.07 A g−1 with a capacity retention of 73.1% even after 500 cycles. The structure and morphology of the composite (90% CuO and 10% Cu/Ga oxides) was successfully retained after 500 cycles, which was confirmed through ex situ XRD, SEM and HRTEM analyses. The composite also exhibited remarkable rate capability in which it delivered 96 mA h g−1 even at a high current density of 6.6 A g−1. The enhanced electrochemical performances of CuO and its gallium composites are attributed to the presence of Cu4O3 and CuGa2O4 phases. The Cu4O3 phase is actively involved in the redox reaction and the CuGa2O4 phase stabilizes the CuO phase and buffers the volume expansion of CuO during cycling. The present approach eplores great opportunities for improving the electrochemical performance of oxide based anode materials for sodium-ion batteries.