NewSoftware Development Engineer III - Amazon Robotics, Autonomous Mobility, AMS Amazon.com Services LLCSoftware Development Engineer III - Amazon Robotics, Autonomous Mobility, AMSNorth Reading, MAThis role offers a unique opportunity to shape the future of autonomous robotics at scale, working with state-of-the-art technologies including real-time robotics systems, machine learning, and agentic AI while seeing your architectural decisions deployed on a production fleet serving millions of customers. • You will play a key role in architecting and implementing next-generation ML and AI-based motion planning and task planning systems, with your work directly impacting thousands of fully autonomous robots operating alongside people in fulfillment centers worldwide.
Cyclotron Engineer SOFIECyclotron EngineerHaverhill, MA$90,000–$100,000 / yearAdditionally, the Cyclotron-Support Engineer I is responsibility for first-line troubleshooting, maintenance, and repair of equipment associated with manufacturing, including manipulator arms, lead shielded hot cells, radiosynthesizers, etc. Perform diagnosis and repair on the following: Electronic equipment, electro-pneumatic systems, high vacuum systems, deionized chilled water systems, high voltage, target, and high-power RF systems.
NewSoftware Development Engineer JobotSoftware Development EngineerBoston, MA$65–$80 / hourDevelopers at this level are building greater independence, taking ownership of small to medium-sized work items, and strengthening their core engineering skills across multiple application layers, including user interfaces, services, APIs, and data. Our teams include professionals across software engineering, product development, clinical informatics, research, and healthcare technology who share a commitment to reducing complexity and improving outcomes for patients and providers.
Sr. Product Engineer – Web Services EsriSr. Product Engineer – Web ServicesBoston, MARemote$93,600–$159,328 / yearExperience working with ArcGIS applications and technologies (such as ArcGIS Hub, ArcGIS Map Viewer, ArcGIS REST APIs, ArcGIS API for Python, ArcGIS Maps SDKs). You will act as a service owner and trusted decision‑maker, shaping priorities, balancing tradeoffs, and ensuring our web services remain reliable, scalable, and valuable to customers over time.
Service Engineer - Industrial Manufacturing - Springfield, MA Michael Page USAService Engineer - Industrial Manufacturing - Springfield, MASpringfield, MA$65,000–$75,000 / yearFull timeThe Service Engineer will spend the majority of their time traveling to customer sites, servicing CNC machines and providing on‑site and remote customer training and support. Program, set up, and train customers on CNC lathes, as well as CNC vertical and horizontal mills, ensuring programs meet customer requirements.
NewProduct Development Engineer SharkNinjaProduct Development EngineerNeedham, MA$86,300–$357,100 / yearSupport the SharkNinja business onsite in our Needham, MA headquarters with the development of successful and profitable programs for key products to ensure continued growth of the product portfolio – you will assist in leading new product development (creation and management) of assigned product(s) from brainstorm phase through mass production, as well as partner with leadership to define the over-arching category direction to a team of product developers. Powered by two trusted, global brands, Shark and Ninja , the company has a proven track record of bringing disruptive innovation to market and developing one consumer product after another has allowed SharkNinja to enter multiple product categories, driving significant growth and market share gains.
Controls Engineer- Building Automation JobotControls Engineer- Building AutomationBoston, MA$90,000–$120,000 / yearAbout the Role: We’re seeking a Building Controls Engineer to support the design, programming, commissioning, and ongoing support of building automation systems (BAS) for commercial clients in the Boston area. Information collected and processed as part of your Jobot candidate profile, and any job applications, resumes, or other information you choose to submit is subject to Jobot's Privacy Policy, as well as the Jobot California Worker Privacy Notice and Jobot Notice Regarding Automated Employment Decision Tools which are available at jobot.com/legal.
NewSales Engineer GCR Professional ServicesSales EngineerAmesbury, Massachusetts$95,000–$120,000 / yearThis role collaborates closely with Sales, Engineering, Operations, and Quality to develop and deliver engineered solutions that meet customer requirements while driving revenue growth, customer satisfaction, and long-term business relationships. The Sales Engineer serves as the technical liaison between customers and internal teams, providing engineering expertise throughout the sales process.
NewDatabase Administrator / Data Engineer - (Accounting/Finance ERP Experience required) JobotDatabase Administrator / Data Engineer - (Accounting/Finance ERP Experience required)Boston, MA$130,000–$160,000 / yearInformation collected and processed as part of your Jobot candidate profile, and any job applications, resumes, or other information you choose to submit is subject to Jobot's Privacy Policy, as well as the Jobot California Worker Privacy Notice and Jobot Notice Regarding Automated Employment Decision Tools which are available at jobot.com/legal. The ideal candidate will have a strong background in database administration, data engineering, and enterprise applications, with experience working with complex financial data, transactional systems, and cloud-based platforms.
Senior Mechanical Engineer SymboticSenior Mechanical EngineerLexington, MAApplying next-gen technology, high-density storage and machine learning to solve today's complex distribution challenges, Symbotic enables companies to move goods with unmatched speed, agility, accuracy and efficiency. Cross-Functional Collaboration: Work closely with electrical, software, controls, manufacturing, and quality engineering teams to ensure seamless integration and product success. .
MS Azure Engineer Continental ResourcesMS Azure EngineerBedford, MAFull timeA successful candidate has strong experience with Azure Cloud services, is self-driven, enjoys learning new technologies, and is willing to stretch themselves to become a stronger engineer and mentor others around them to do the same. Developing effective cloud infrastructure, enforcing good architectural principles, providing technical oversight, and ensuring security best practices are implemented and followed.
NewLead, Electro-Optical (EO) Systems Engineer : Sign-on bonus ($30K max) L3Harris TechnologiesLead, Electro-Optical (EO) Systems Engineer : Sign-on bonus ($30K max)Wilmington, MA$127,500–$236,500 / yearThe successful candidate will support the program technical leads (Lead or Chief Systems Engineer, IPT Lead) by performing technical analysis, managing specifications, and generating design review and technical documents. L3Harris is a proven leader in tactical communications, geospatial systems and services, air traffic management, environmental solutions, avionics and electronic warfare, and space and intelligence.
CAD / PCB Engineer II GCR Professional ServicesCAD / PCB Engineer IIAndover, MassachusettsContractorJoin a focused team of engineers bringing highly complex, dense, rugged and secure electronic packaging solutions to our nation’s warfighters and first responders. • Ability to work in a fast-paced engineering services group supporting multiple time zones within the US and internationally.
NewApplication Engineer GCR Professional ServicesApplication EngineerBillerica, Massachusetts$95,000–$130,000 / yearJob Summary: This role is responsible for translating customer technical requirements into product specifications, designing and validating new features, and developing custom mechanical components. It also includes maintaining technical documentation, providing on-site support, and collaborating cross-functionally to ensure successful product implementation.
NewGeneral/Interdisciplinary Engineer, Senior - Secret DCS CorporationGeneral/Interdisciplinary Engineer, Senior - SecretBedford, MA$90,220–$170,000 / yearConduct systems architectural analyses to include system design/design feasibility and state-of-the-art assessment to Produce architectures, document planned and existing systems, determine deficiencies, develop alternatives, recommend solutions, and support development of a plan to implement the chosen solution per acquisition and sustainment system engineering processes. Analysis of Alternatives (AoA), Systems Engineering Plan (SEP)…), systems review and analysis with written reporting, briefing, and artifact development as required for all of the technical specialty areas defined in this section; and the planning and execution of all necessary technical reviews, assessments, and interchange meetings (e.g.
NewRF Engineer Butler America AerospaceRF EngineerMaynard, MA$82–$97 / hourContractorExpertise with RF subsystems and hardware including antennas, transmitters, receivers, microwave components, low noise amplifiers, high power amplifiers, advanced electronic modules, amplifiers, mixers, switches, frequency generation circuits, and frequency conversion circuits is desired. -The engineering will collaborate with other engineering disciplines including hardware engineers, systems engineers, and circuit design engineers as well as technical and manufacturing support personnel.
NewRF Engineer PlanIT GroupRF EngineerChelmsford, MAExpertise with RF subsystems and hardware including antennas, transmitters, receivers, microwave components, low noise amplifiers, high power amplifiers, advanced electronic modules, amplifiers, mixers, switches, frequency generation circuits, and frequency conversion circuits is desired. Basic Minimum Requirements: • Bachelor of Science Degree in Electrical Engineering preferred or BS Degree in Science, Technology, Engineering, or Math (STEM) accepted plus a minimum of 5+ years of relevant professional engineering experience.
NewInfrastructure Cloud Engineer Kforce Inc.Infrastructure Cloud EngineerWilmington, MA$63–$72Employee pay is based on factors like relevant education, qualifications, certifications, experience, skills, seniority, location, performance, union contract and business needs. By clicking “Apply Today” you agree to receive calls, AI-generated calls, text messages or emails from Kforce and its affiliates, and service providers.
Senior Lead AI Software Engineer KlaviyoSenior Lead AI Software EngineerBoston, MA$216,000–$324,000 / yearAs a Senior Lead Software Engineer on Amplify, you will: Independently own and drive high-impact objectives that span multiple Amplify teams and align with company priorities, defining the technical roadmap that ensures our internal applications, APIs, data and event pipelines, and AI-powered workflows can scale with Klaviyo and continue delivering measurable business outcomes. Independently lead the end-to-end lifecycle of large, multi-team initiatives with clear technical direction, architectural leadership, and active workstream curation, from discovery and design through implementation, rollout, and long-term ownership of complex programs that span internal customers across the company.
NewSr. Engineer - TS Clearance System OneSr. Engineer - TS ClearanceBedford, MA$155,000–$175,000 / hourSupport digital engineering concepts and techniques throughout the program lifecycle, including Model Based Systems Engineering (MBSE). System One, and its subsidiaries including Joulé and Mountain Ltd., are leaders in delivering outsourced services and workforce solutions across North America.
NewELECTRICAL ENGINEER IV System OneELECTRICAL ENGINEER IVTewksbury, MA$97.33 / hour10+ years designing and developing hardware solutions, including FPGA/VHDL, Altium, Xilinx ISE14.4, Linux, Ethernet, I2C, SPI. System One, and its subsidiaries including Joulé and Mountain Ltd., are leaders in delivering outsourced services and workforce solutions across North America.
NewSystems Engineer - TS Clearance System OneSystems Engineer - TS ClearanceBedford, MA$140,000–$150,000 / hourConduct reviews on program portfolio to evaluate and/or recommend alternative plans, improve systems engineering programs/processes, manage/sustain program technical baseline, and design/perform system level tests to ensure subsystem and system performance in accordance with specifications. Perform program reviews to evaluate proposed plans, systems engineering programs, design, and test results, ensuring performance is met per program requirements.
Director, AI Engineer KPMGDirector, AI EngineerBoston, MADeep understanding of scaling AI-driven solutions, ethical AI, and MLOps practices for maintaining models; ability to bring industry consulting insights with a balance of technical and business acumen to deliver strategic, value-driven AI solutions; In-depth knowledge of AI orchestration and best practices. Proficient in architecting and implementing AI-powered workflow solutions using Microsoft, AWS, or Google Cloud services (For example: Foundry, Bedrock, Vertex AI), with capabilities in defining blueprints and technical requirements for scalable, automated systems with expertise in agentic AI and automation.
for Desktop Support Engineer (Window 11 Upgrade) Tanisha Systemsfor Desktop Support Engineer (Window 11 Upgrade)Plymouth, MAContractorRequired Technical and Professional Expertise: 6 + years’ experience customer service and support of Windows Operating systems in a global enterprise environment from both software and hardware troubleshooting standpoint. Monitor and analyse gaps building processes to rationalize, troubleshoot and escalate technical problems with endpoint management clients, client inventory, application deployments and security patching.
Systems Engineer, Junior - TS DCS CorporationSystems Engineer, Junior - TSBedford, MA$73,160–$115,000 / yearThe C2ISR Division provides worldwide life cycle support across the spectrum of the C2ISR capabilities based enterprise; including supply, distribution, materiel management, acquisition, system engineering and maintenance, financial planning and budgeting, security, flight test, and contracting functions. Experienced in requirements development, production and deployment, and operation and support, architectures development & implementation, modeling & simulation including but not limited to Model Based Systems Engineering principles, verification & validation, technical data package development and sustainment, and principles of configuration management.
Senior AI Engineer - Customer Agent KlaviyoSenior AI Engineer - Customer AgentBoston, MA$148,000–$222,000 / yearIn addition to base salary, our total compensation package may include participation in the company’s annual cash bonus plan, variable compensation (OTE) for sales and customer success roles, equity, sign-on payments, and a comprehensive range of health, welfare, and wellbeing benefits based on eligibility. We have a big opportunity to build state-of-the-art AI and machine learning technologies at Klaviyo to power our products and develop AI agents that can automatically create and execute marketing or customer experiences, strategies, and campaigns for any business.
Product Engineer II – Utility Solutions EsriProduct Engineer II – Utility SolutionsBoston, MARemote$79,664–$133,120 / yearAs the Product Engineer II – Utilities, you will collaborate with customers, industry teams, and other product development team members to design, develop, and support the right geospatial solutions for electric, gas, water, sewer, stormwater and telecommunications agencies. Design and author test cases for functionality, performance, scalability, and durability; execute both manual and automated tests, analyze test results, and report results.
Technical Sales & Support Engineer Pinnacle Technical ResourcesTechnical Sales & Support EngineerAgawam, Massachusetts$70,000–$90,000 / yearThe specific compensation for this position will be determined by several factors, including the scope, complexity, and location of the role, as well as the cost of labor in the market; the skills, education, training, credentials, and experience of the candidate; and other conditions of employment. Based on-site in Agawam, MA, this role assists in managing the technical lifecycle of GAC products by delivering expert sales support and field service via phone or in person.
Software Engineer (C# .NET Framework/SQL Server) SarnovaSoftware Engineer (C# .NET Framework/SQL Server)Boston, MAThe position is well suited for an engineer who enjoys working with complex systems, troubleshooting production issues, and contributing to the continued evolution and sustainability of the platform. This role focuses on supporting, enhancing, and progressively modernizing enterprise and legacy applications using C#, NET Framework, and SQL Server.
Sr. Lead AI Engineer KlaviyoSr. Lead AI EngineerBoston, MA$216,000–$324,000 / yearYou’ll own architecture and execution for complex, distributed backend systems; guide other engineers through design and implementation; and partner closely with product, machine learning, and data science to turn AI ideas into reliable, scalable production capabilities. You’ve built and shipped generative or agentic AI applications (e.g., LLM‑backed flows, tool‑using agents, retrieval‑augmented systems) and are comfortable with prompt design, few‑shot approaches, fine‑tuning, and evaluation.
Manager, Cloud Engineer - Terraform KPMGManager, Cloud Engineer - TerraformBoston, MAQualifications: Minimum five years of recent experience in IT infrastructure technology management and architecture including IaaS/PaaS/DevOps cloud transformation programs and infrastructure automation, prior system/storage; admin/engineering experience and consulting experience; four years of cloud strategy, migration, and transformation leadership including cloud services (IaaS/PaaS) implementation & migration, including Azure or AWS. Additional desirable experience in infrastructure automation and instrumentation (Unix Admin, Scripting / Programming Capabilities, SDLC Process Knowledge), Unified Communications, Collaboration, Database/application server architecture, network, information security, GenAI, RAG.
NewSenior Associate, Privileged Access Management Delivery Engineer KPMGSenior Associate, Privileged Access Management Delivery EngineerBoston, MA$95,855–$208,265 / yearImplement and maintain PAM capabilities including privileged credential management, session management, just-in-time access, and endpoint management (EPM)components; implement automated integration across adjacent security solutions (for example: Crowdstrike, SIEM solutions, ServiceNow); automate PAM tasks using scripting and APIs (such as PowerShell, Python, REST, and others) and integrate with enterprise platforms (that is, Active Directory, IdPs, ITSM platforms, SIEM platforms, and more). Hands on experience with Privileged Access Management delivery and engineering, with specific experience using CyberArk On-Prem and SaaS solutions; additional experience with secrets management platforms (that is, Conjur, HashiCorp) and other PAM platforms (such as Delinea, BeyondTrust) preferred.
NewPrincipal Electrical Engineer # 26-17099 US Tech Solutions, Inc.Principal Electrical Engineer # 26-17099Westford, MAPosition Overview: This is a critical role supporting the OCT product line, primarily focused on sustaining engineering activities and addressing end-of-life components for legacy products. The position requires a hands-on electrical engineer who can quickly contribute to electrical and electronic design efforts and provide technical guidance on complex projects.
Principal Software Engineer, Enterprise Scalability KlaviyoPrincipal Software Engineer, Enterprise ScalabilityBoston, MA$244,000–$366,000 / yearAI‑assisted scale engineering: AI‑driven anomaly detection reduces alert noise while improving signal; generative load testing and copilot runbooks are used in release/readiness checks for the top critical services; time‑to‑isolate regressions drops 20–30%. In addition to base salary, our total compensation package may include participation in the company’s annual cash bonus plan, variable compensation (OTE) for sales and customer success roles, equity, sign-on payments, and a comprehensive range of health, welfare, and wellbeing benefits based on eligibility.
Senior Software Engineer - Growth KlaviyoSenior Software Engineer - GrowthBoston, MA$148,000–$222,000 / yearYou will define the architectural approach and technical strategy for your area of responsibility, anticipating scalability and reliability needs, including leveraging AI agents in our work and delivery, ensuring the solution is robust, scalable, and adheres to best practices for security, performance, and maintainability. In addition to base salary, our total compensation package may include participation in the company’s annual cash bonus plan, variable compensation (OTE) for sales and customer success roles, equity, sign-on payments, and a comprehensive range of health, welfare, and wellbeing benefits based on eligibility.
Principal Engineer, Core Infrastructure KlaviyoPrincipal Engineer, Core InfrastructureBoston, MA$244,000–$366,000 / yearIn addition to base salary, our total compensation package may include participation in the company’s annual cash bonus plan, variable compensation (OTE) for sales and customer success roles, equity, sign-on payments, and a comprehensive range of health, welfare, and wellbeing benefits based on eligibility. AI‑enabled platform: Approved AI tooling is integrated into IDE/CI/CD with repo policies and auditability; ≥70% MAU among eligible engineers; MTTR down 20–30% via AI‑assisted triage; flaky‑test rate decreases through targeted, AI‑suggested fixes.
NewSenior Process Engineer - Manufacturing - Pembroke, MA Michael Page USASenior Process Engineer - Manufacturing - Pembroke, MAPembroke, MA$110,000–$145,000 / yearFull timeThis role combines hands-on engineering expertise with project leadership, supporting continuous improvement initiatives, equipment upgrades, and new product commercialization efforts. The Senior Process Engineer is responsible for developing, optimizing, and sustaining plastics compounding and extrusion processes to improve safety, quality, productivity, and profitability.
CNC Manufacturing Engineer - Industrial - Salisbury, MA Michael Page USACNC Manufacturing Engineer - Industrial - Salisbury, MASalisbury, MA$90,000–$110,000 / yearFull timeThe CNC Manufacturing Engineer will report directly into the Engineering Manager and be responsible for: Develop, optimize, and troubleshoot CNC programs for multi-axis mills and lathes (primarily using Siemens NX). My client is seeking a highly skilled CNC Programmer/Manufacturing Engineer that will combine hands-on CNC programming with broader manufacturing engineering responsibilities.
Senior Electrical Engineer - Industrial - Danvers, MA Michael Page USASenior Electrical Engineer - Industrial - Danvers, MADanvers, MA$125,000–$180,000 / yearFull timeMy client is a global technology leader in semiconductor manufacturing equipment, providing innovative solutions that enable the production of advanced chips used in consumer electronics, automotive applications, communications, and industrial technologies. The Senior Electrical Engineer is responsible for the design, development, and support of complex electrical and electromechanical systems used in advanced semiconductor manufacturing equipment.
Senior Full Stack Engineer - Customer Agent KlaviyoSenior Full Stack Engineer - Customer AgentBoston, MA$148,000–$222,000 / yearIn addition to base salary, our total compensation package may include participation in the company’s annual cash bonus plan, variable compensation (OTE) for sales and customer success roles, equity, sign-on payments, and a comprehensive range of health, welfare, and wellbeing benefits based on eligibility. As a Senior Engineer, you’ll tackle complex challenges, develop multiple solutions, and evaluate business and technical trade-offs to determine the best path forward.
Senior Software Engineer, Agent Platform KlaviyoSenior Software Engineer, Agent PlatformBoston, MA$148,000–$222,000 / yearIn addition to base salary, our total compensation package may include participation in the company’s annual cash bonus plan, variable compensation (OTE) for sales and customer success roles, equity, sign-on payments, and a comprehensive range of health, welfare, and wellbeing benefits based on eligibility. We have a big opportunity to build state-of-the-art AI and machine learning technologies at Klaviyo to power our products and develop AI agents that can automatically create and execute marketing or customer experiences, strategies, and campaigns for any business.
Manager, AI Marketing Orchestration, GTM Engineer SarnovaManager, AI Marketing Orchestration, GTM EngineerBoston, MAThis role transforms marketing from a manual, channel-driven function into a scalable, AI-powered growth engine by automating execution, improving speed to market, and increasing efficiency across campaigns. The Manager, AI Marketing Orchestration will design, build, and optimize agentic marketing workflows that drive scalable growth across email, paid media, data and content.
FM Approvals Electrical Engineer FMFM Approvals Electrical EngineerNorwood, MA$94,000–$134,000As a trusted leader in third-party certification, we help manufacturers bring safe, compliant, and high-performing products to market. Here, you’ll grow your technical expertise, collaborate with industry experts, and play a key role in advancing global safety.
NewSenior Process Engineer Michael Page USASenior Process EngineerRockland, MA$120,000–$145,000 / yearFull timeBachelor's degree in Chemical Engineering, Plastics Engineering, Materials Science, Mechanical Engineering, Manufacturing Engineering, or a related engineering discipline. This position combines hands-on engineering expertise, project management, and new product commercialisation responsibilities to improve safety, quality, productivity, and profitability.
Lab Calibration Technician Diedre Moire Corp.Lab Calibration TechnicianTaunton, MA$90,000–$140,000 / yearFull timeCONSIDERED EXPERIENCE INCLUDES: Metrologist Maintenance Calibration Technician Metrology Analytical Laboratory Instrumentation Validation Chromatography Mass Spectrometry HPLC UPLC GC MS GC/MS Chemistry Analyzers #DiedreMoire #JobSearch #JobHunt #JobOpening #Hiring #Job #Jobs #Careers #Employment #fieldservicejobs #technicianjobs #LabTechnicianJobs #MetrologistJobs #CalibrationTech. Leader in Liquid Chromatography-Mass Spectrometry and Capillary Electrophoresis-Mass Spectrometry, supporting clinical research, drug discovery, food and environmental testing, and forensic toxicology looking to hire Field Service Engineer to support LCMS platforms.
Field Service Engineer (Boston) StratAcuity Staffing Partners IncField Service Engineer (Boston)Needham, MAComplete and ensure proper distribution and storage of all required Work Order forms, Site Acceptance Test documentation, radiation survey documentation and other documents per company policy, including any specific customer contractual requirements (as needed). It is the responsibility of every employee to report to their manager or a member of senior management any quality problems or defects in order for corrective action to be implemented and to avoid recurrence of the problem.
Field Service Engineer - Generators elix sourcing solutionsField Service Engineer - GeneratorsSouthampton, Hampshire£35,000–£40,000This role would suit a Field Service Engineer with a background working on Generators looking to work for a leading company in their field who are looking to continue that success and can offer a role with a variety of clients, company benefits such as bonuses and overtime to greatly increase yearly salary. Field Service Engineer | FSE | Service Engineer |Generator Engineer | Depot Engineer | Engineer | Generators | Diesel Engines | Electrical | Servicing | Hampshire | Southampton | Portsmouth | Eastleigh | Winchester | Bournemouth.
Field Service Engineer - White Goods, Laundry elix sourcing solutionsField Service Engineer - White Goods, LaundryBristol, Bristol£36,000–£39,000Service Engineer, Mobile Engineer, Field Service, Technician, White Goods, Catering, Coffee, Dishwasher, Domestic Appliances, Glasswasher, Comcat, Commercial, Laundry, Refrigeration, Electrical, 18th, Bristol, Swindon, Bath, Weston, Clevedon, This is a regional role, paid door to door, servicing, repairing and maintaining commercial laundry equipment, there is a weekend call out rota 1 in 4 weekends with additional payments and overtime rates applied.
Field Service Engineer Gator Bio IncField Service EngineerBoston, MA$90,000–$120,000 / yearThe Gator instrument suite, including models such as the Gator Pro, Pivot, Prime, Pilot, and Plus, empower researchers across diverse applications, from antibody discovery to small molecule analysis. Gator Bio is at the forefront of biolayer interferometry (BLI) technology, delivering real-time, label-free analysis systems to support breakthroughs in biomolecular interactions.