Deep Reinforcement Learning with Python. Master classic RL, deep RL, distributional RL, inverse RL, and more with OpenAI Gym and TensorFlow - Second Edition

Sudharsan Ravichandiran

With significant enhancements in the quality and quantity of algorithms in recent years, this second edition of Hands-On Reinforcement Learning with Python has been revamped into an example-rich guide to learning state-of-the-art reinforcement learning (RL) and deep RL algorithms with TensorFlow 2 and the OpenAI Gym toolkit.In addition to exploring RL basics and foundational concepts such as Bellman equation, Markov decision processes, and dynamic programming algorithms, this second edition dives deep into the full spectrum of value-based, policy-based, and actor-critic RL methods. It explores state-of-the-art algorithms such as DQN, TRPO, PPO and ACKTR, DDPG, TD3, and SAC in depth, demystifying the underlying math and demonstrating implementations through simple code examples.The book has several new chapters dedicated to new RL techniques, including distributional RL, imitation learning, inverse RL, and meta RL. You will learn to leverage stable baselines, an improvement of OpenAI’s baseline library, to effortlessly implement popular RL algorithms. The book concludes with an overview of promising approaches such as meta-learning and imagination augmented agents in research.By the end, you will become skilled in effectively employing RL and deep RL in your real-world projects.

Mastering Flask Web and API Development. Build and deploy production-ready Flask apps seamlessly across web, APIs, and mobile platforms

Sherwin John C. Tragura

Flask is a popular Python framework known for its lightweight and modular design. Mastering Flask Web and API Development will take you on an exhaustive tour of the Flask environment and teach you how to build a production-ready application.You’ll start by installing Flask and grasping fundamental concepts, such as MVC and ORM database access. Next, you’ll master structuring applications for scalability through Flask blueprints. As you progress, you’ll explore both SQL and NoSQL databases while creating REST APIs and implementing JWT authentication, and improve your skills in role-based access security, utilizing LDAP, OAuth, OpenID, and databases. The new project structure, managed by context managers, as well as ASGI support, has revolutionized Flask, and you’ll get to grips with these crucial upgrades. You'll also explore out-of-the-box integrations with technologies, such as RabbitMQ, Celery, NoSQL databases, PostgreSQL, and various external modules. The concluding chapters discuss enterprise-related challenges where Flask proves its mettle as a core solution.By the end of this book, you’ll be well-versed with Flask, seeing it not only as a lightweight web and API framework, but also as a potent problem-solving tool in your daily work, addressing integration and enterprise issues alongside Django and FastAPI.

Learning Design Patterns with Unity. Learn the secret of popular design patterns while building fun, efficient games in Unity 2023 and C#

Harrison Ferrone

Struggling to write maintainable and clean code for your Unity games? Look no further! Learning Design Patterns with Unity empowers you to harness the fullest potential of popular design patterns while building exciting Unity projects. Through hands-on game development, you'll master creational patterns like Prototype to efficiently spawn enemies and delve into behavioral patterns like Observer to create reactive game mechanics. As you progress, you'll also identify the negative impacts of bad architectural decisions and understand how to overcome them with simple but effective practices. By the end of this Unity 2023 book, the way you develop Unity games will change. You'll emerge not just as a more skilled Unity developer, but as a well-rounded software engineer equipped with industry-leading design patterns.

Drupal 8 Theming with Twig. Master Drupal 8’s new Twig templating engine to create fun and fast websites with simple steps to help you move from concept to completion

Chaz Chumley

Drupal 8 is an open source content management system and powerful framework that helps deliver great websites to individuals and organizations, including non-profits, commercial, and government around the globe. This new release has been built on top of object-oriented PHP and includes more than a handful of improvements such as a better user experience, cleaner HTML5 markup, a new templating engine called Twig, multilingual capabilities, new configuration management, and effortless content authoring. Drupal 8 will quickly become the new standard for deploying content to both the web and mobile applications. However, with so many new changes, it can quickly become overwhelming knowing where to start and how to quickly.Starting from the bottom up, we will install, set up, and configure Drupal 8. We’ll navigate the Admin interface so you can learn how to work with core themes and create new custom block layouts. Walk through a real-world project to create a Twig theme from concept to completion while adopting best practices to implement CSS frameworks and JavaScript libraries. We will see just how quick and easy it is to create beautiful, responsive Drupal 8 websites while avoiding the common mistakes that many front-end developers make.

Learning Shiny. Make the most of R’s dynamic capabilities and implement web applications with Shiny

Hernan Resnizky

Puppet 3 Cookbook. An essential book if you have responsibility for servers. Real-world examples and code will give you Puppet expertise, allowing more control over servers, cloud computing, and desktops. A time-saving, career-enhancing tutorial - Second Edition

John Arundel

A revolution is happening in web operations. Configuration management tools can build servers in seconds, and automate your entire network. Tools like Puppet are essential to taking full advantage of the power of cloud computing, and building reliable, scalable, secure, high-performance systems. More and more systems administration and IT jobs require some knowledge of configuration management, and specifically Puppet.Puppet 3 Cookbook takes you beyond the basics to explore the full power of Puppet, showing you in detail how to tackle a variety of real-world problems and applications. At every step it shows you exactly what commands you need to type, and includes full code samples for every recipe.The book takes the reader from a basic knowledge of Puppet to a complete and expert understanding of Puppet's latest and most advanced features, community best practices, writing great manifests, scaling and performance, and extending Puppet by adding your own providers and resources. It starts with guidance on how to set up and expand your Puppet infrastructure, then progresses through detailed information on the language and features, external tools, reporting, monitoring, and troubleshooting, and concludes with many specific recipes for managing popular applications.The book includes real examples from production systems and techniques that are in use in some of the world's largest Puppet installations, including a distributed Puppet architecture based on the Git version control system. You'll be introduced to powerful tools that work with Puppet such as Hiera. The book also explains managing Ruby applications and MySQL databases, building web servers, load balancers, high-availability systems with Heartbeat, and many other state-of-the-art techniques

Learning RSLogix 5000 Programming. Build robust PLC solutions with ControlLogix, CompactLogix, and Studio 5000/RSLogix 5000 - Second Edition

Austin Scott, Austin Scott

Understanding programmable logic controller (PLC) programming with Rockwell Software’s Logix Designer and the Studio 5000 platform, which includes ControlLogix, CompactLogix, and SoftLogix, is key to building robust PLC solutions. RSLogix 5000/Studio 5000’s Logix Designer are user-friendly IEC 61131-3-compliant interfaces for programming the current generation of Rockwell Automation Controllers using Ladder Diagram (LD), Function Block Diagram (FBD), Structured Text (ST), and Sequential Function Chart (SFC).This second edition of Learning RSLogix 5000 Programming guides you through the technicalities and comes packed with the latest features of Studio 5000, industrial networking fundamentals, and industrial cybersecurity best practices. You’ll go through the essential hardware and software components of Logix, before learning all about the new L8 processor model and the latest Studio 5000 architecture to build effective integrated solutions. Entirely new for this edition, you’ll discover a chapter on cybersecurity concepts with RSLogix 5000. The book even gets you hands-on with building a robot bartender control system from start to finish.By the end of this Logix 5000 book, you’ll have a clear understanding of the capabilities of the Logix platform and be able to confidently navigate Rockwell Automation Literature Library resources.

Ext.NET Web Application Development. If you’re looking to build .NET based rich internet applications, look no further. This is the ideal primer that takes you step by step through the practical aspects of combining Ext.NET and Ext JS, and much more

Anup K Shah, Anup Shah

To build a rich internet application, you need to integrate a powerful client side JavaScript framework with a server side framework. Ext.NET achieves this by integrating Sencha's Ext JS framework with the power of ASP.NET. The result ñ a sophisticated framework offering a vast array of controls, layout, and powerful AJAX and server bindings, which can be used to build rich, highly usable web applications.Ext.NET Web Application Development shows you how to build rich applications using Ext.NET. Examples guide you through Ext.NET's various components using both ASP.NET Web Forms and MVC examples. You will also see how Ext.NET handles data binding and server integration. You will also learn how to create reusable components and put them together in great looking applications.This book guides you through the various Ext.NET components and capabilities to enable you to create highly usable Ext.NET components and web applications.You will learn about various UI components and numerous layout options through examples. You will see how the AJAX architecture enables you to create powerful data-oriented applications easily. This book will also teach you how to create reusable custom components to suit your needs.Ext.NET Web Application Development shows you how to create rich and usable applications using Ext.NET through numerous examples.

Scientific Computing with Scala. Learn to solve scientific computing problems using Scala and its numerical computing, data processing, concurrency, and plotting libraries

Vytautas Jancauskas

Scala is a statically typed, Java Virtual Machine (JVM)-based language with strong support for functional programming. There exist libraries for Scala that cover a range of common scientific computing tasks – from linear algebra and numerical algorithms to convenient and safe parallelization to powerful plotting facilities. Learning to use these to perform common scientific tasks will allow you to write programs that are both fast and easy to write and maintain.We will start by discussing the advantages of using Scala over other scientific computing platforms. You will discover Scala packages that provide the functionality you have come to expect when writing scientific software. We will explore using Scala's Breeze library for linear algebra, optimization, and signal processing. We will then proceed to the Saddle library for data analysis. If you have experience in R or with Python's popular pandas library you will learn how to translate those skills to Saddle. If you are new to data analysis, you will learn basic concepts of Saddle as well. Well will explore the numerical computing environment called ScalaLab. It comes bundled with a lot of scientific software readily available. We will use it for interactive computing, data analysis, and visualization. In the following chapters, we will explore using Scala's powerful parallel collections for safe and convenient parallel programming. Topics such as the Akka concurrency framework will be covered. Finally, you will learn about multivariate data visualization and how to produce professional-looking plots in Scala easily. After reading the book, you should have more than enough information on how to start using Scala as your scientific computing platform

Oracle Hyperion Interactive Reporting 11 Expert Guide. Learn Advanced Dashboards, JavaScript, Computations, and Special Topics from the Experts

Edward J. Cody, Emily M. Vose, Emily Vose, Edward Cody

Oracle Hyperion Interactive Reporting is one of many products in the Oracle Business Intelligence Enterprise Edition Plus software suite, an industry-leading business intelligence platform. The primary focus of the Interactive Reporting product is to provide strong relational querying and data analysis capabilities, where the software provides significant flexibility for creating custom dashboards, interfaces, and data analysis routines through the use of JavaScript programming and built-in software functionality. While Interactive Reporting is extremely flexible, performing advanced operations in the software is complicated and requires basic programming knowledge and an advanced understanding of the software. This book continues from where The Business Analyst’s Guide to Oracle Hyperion Interactive Reporting 11 completed and provides the reader with the information to successfully execute the advanced features of the product along with examples and specific techniques applicable to everyday use.The Oracle Hyperion Interactive Reporting 11 Expert Guide provides software users and developers with many examples of the techniques used by software experts. The book begins with an introduction to leveraging advanced features of the project and an introduction to JavaScript. Dashboards are a major focus of the book with four chapters focused on building a simple to complex dashboard including functions, global objects, and syncing selections across dashboards. The book places an emphasis on learning methods for data analysis by using advanced programming and built-in functions, and a unique approach to using code to generate batch reports and exports is provided. The Dashboard Studio Optimize Utility and the Dashboard Studio Merge utility are explained in detail, and the approach to building and using a central code repository for use in dashboards and computations across multiple documents in an enterprise is demonstrated. This book will help the reader become an expert user of the software, providing the skills necessary to understand, communicate, and perform advanced level tasks. The authors’ experience in developing and supporting Interactive Reporting users is very apparent throughout each chapter of the book. While the book displays content and examples from version 11 of the software, the book is also applicable to previous versions of the software dating back to version 8, so readers not currently using Interactive Reporting 11 will find the book applicable to daily use with the product.

WordPress 3 Search Engine Optimization. Getting your WordPress site well positioned on Google and Bing is a fine art that this guide covers brilliantly. From SEO basics to white-hat tips and tricks, you’ll learn to give your site the competitive edge

Michael David, Michael David

WordPress is a powerful platform for creating feature-rich and attractive websites and blogs; but with a little extra tweaking and effort your WordPress site can dominate the search engines and bring thousands of new customers to your blog or business.WordPress3.0 Search Engine Optimization will show you the secrets that professional SEO companies use to take websites to the top of search results and proliferate their business. You'll be able to take your WordPress blog/site to the next level, as well as brush aside even the stiffest competition with this book in hand.We'll begin with a typical WordPress installation and with a variety of simple techniques, turn it into a powerful website that search engines will reward with high rankings.We'll go further: with advanced plug-ins we'll connect your WordPress site to popular social media sites and expand the reach of your site to bring more visitors. You'll learn about dozens of free online tools to accomplish everything from keyword research to monitoring your ranking progress.WordPress is a great start for building search-friendly sites. However, with the tools in this book, you'll get your website/blog noticed by numerous new users/customers or your target audience.

Vue.js 3 Cookbook. Discover actionable solutions for building modern web apps with the latest Vue features and TypeScript

Heitor Ramon Ribeiro

Vue.js is a progressive web framework for building professional user interfaces for your web applications. With Vue.js 3, the frontend framework is reinforced with architectural enhancements, new base languages, new render processes, and separated core components.The book starts with recipes for implementing Vue.js 3’s new features in your web development projects and migrating your existing Vue.js apps to the latest version. You will get up and running with TypeScript with Vue.js and find succinct solutions to common challenges and pitfalls faced in implementing components, derivatives, and animation, through to building plugins, adding state management, routing, and developing complete single-page applications (SPAs). As you advance, you'll discover recipes to help you integrate Vue.js apps with Nuxt.js in order to add server-side rendering capabilities to your SPAs. You'll then learn about the Vue.js ecosystem by exploring modern frameworks such as Quasar, Nuxt.js, Vuex, and Vuetify in your web projects. Finally, the book provides you with solutions for packaging and deploying your Vue.js apps.By the end of this Vue.js book, you'll be able to identify and solve challenges faced in building Vue.js applications and be able to adopt the Vue.js framework for frontend web projects of any scale.

Apache Hive Essentials. Immerse yourself on a fantastic journey to discover the attributes of big data by using Hive

Dayong Du

ActionScript Graphing Cookbook. Learn how to create appealing and interactive visual presentations of your data in ActionScript with this book and

Peter Backx, Dominic Gelineau

A picture is worth a thousand words has never been more true than when representing large sets of data. Bar charts, heat maps, cartograms, and many more have become important tools in applications and presentations to quickly give insight into complicated issues.The ActionScript Graphing Cookbook shows you how to add your own charts to any ActionScript program. The recipes give step-by-step instructions on how to process the input data, how to create various types of charts and how to make them interactive for even more user engagement.Starting with basic ActionScript knowledge, you will learn how to develop many different types of charts.First learn how to import your data, from Excel, web services and more. Next process the data and make it ready for graphical display. Pick one of the many graph options available as the book guides you through ActionScript's drawing functions. And when you're ready for it, branch out into 3D display.The recipes in the ActionScript Graphing Cookbook will gradually introduce you into the world of visualization.

Artificial Intelligence for Robotics. Build intelligent robots using ROS 2, Python, OpenCV, and AI/ML techniques for real-world tasks - Second Edition

Francis X. Govers III, Dr. Kamesh Namuduri

Unlock the potential of your robots by enhancing their perception with cutting-edge artificial intelligence and machine learning techniques. From neural networks to computer vision, this second edition of the book equips you with the latest tools, new and expanded topics such as object recognition and creating artificial personality, and practical use cases to create truly smart robots.Starting with robotics basics, robot architecture, control systems, and decision-making theory, this book presents systems-engineering methods to design problem-solving robots with single-board computers. You'll explore object recognition using YOLO and genetic algorithms to teach your robot to identify and pick up objects, leverage natural language processing to give your robot a voice, and master neural networks to classify and separate objects and navigate autonomously, before advancing to guiding your robot arms using reinforcement learning and genetic algorithms. The book also covers path planning and goal-oriented programming to prioritize your robot's tasks, showing you how to connect all software using Python and ROS 2 for a seamless experience.By the end of this book, you'll have learned how to transform your robot into a helpful assistant with NLP and give it an artificial personality, ready to tackle real-world tasks and even crack jokes.

AWS for Solutions Architects. The definitive guide to AWS Solutions Architecture for migrating to, building, scaling, and succeeding in the cloud - Second Edition

Saurabh Shrivastava, Neelanjali Srivastav, Alberto Artasanchez, Imtiaz Sayed, ...

Are you excited to harness the power of AWS and unlock endless possibilities for your business? Look no further than the second edition of AWS for Solutions Architects! Imagine crafting cloud solutions that are secure, scalable, and optimized – not just good, but industry-leading.This updated guide throws open the doors to the AWS Well-Architected Framework, design pillars, and cloud-native design patterns empowering you to craft secure, performant, and cost-effective cloud architectures. Tame the complexities of networking, conquering edge deployments and crafting seamless hybrid cloud connections. Uncover the secrets of big data and streaming with EMR, Glue, Kinesis, and MSK, extracting valuable insights from data at speeds you never thought possible. Future-proof your cloud with game-changing insights! New chapters unveil CloudOps, machine learning, IoT, and blockchain, empowering you to build transformative solutions. Plus, unlock the secrets of storage mastery, container excellence, and data lake patterns. From simple configurations to sophisticated architectures, this guide equips you with the knowledge to solve any cloud challenge and impress even the most demanding clients.This book is your one-stop shop for architecting industry-standard AWS solutions. Stop settling for average – dive in and build like a pro!

R for Data Science Cookbook. Over 100 hands-on recipes to effectively solve real-world data problems using the most popular R packages and techniques

Yu-Wei, Chiu (David Chiu)

This cookbook offers a range of data analysis samples in simple and straightforward R code, providing step-by-step resources and time-saving methods to help you solve data problems efficiently.The first section deals with how to create R functions to avoid the unnecessary duplication of code. You will learn how to prepare, process, and perform sophisticated ETL for heterogeneous data sources with R packages. An example of data manipulation is provided, illustrating how to use the “dplyr” and “data.table” packages to efficiently process larger data structures. We also focus on “ggplot2” and show you how to create advanced figures for data exploration.In addition, you will learn how to build an interactive report using the “ggvis” package. Later chapters offer insight into time series analysis on financial data, while there is detailed information on the hot topic of machine learning, including data classification, regression, clustering, association rule mining, and dimension reduction.By the end of this book, you will understand how to resolve issues and will be able to comfortably offer solutions to problems encountered while performing data analysis.

Creating Templates with Artisteer. Why pay for a professional website when you can do it yourself with this hands-on guide to Artisteer? With no need for HTML, web-programming, or drawing skills, this book is all you require to create fantastic CMS templates

Jakub Sanecki

Designing good looking, professional quality web templates or building your own website are rather complicated tasks, demanding a lot of technical and graphical expertise. Artisteer has changed this situation, enabling you to do it by yourself, without the need to learn skills such as HTML, web-programming languages, or drawing.Creating stunning Templates with Artisteer is a practical, step-by-step guide that will show you how you can prepare an elegant, professional looking website, on your own, using features of Artisteer. It also describes the process of designing templates for various popular CMS platforms like WordPress or Joomla!, by giving you practical hints, showing how to install those templates and how to import the content into CMS. Creating stunning Templates with Artisteer leads you through the process of designing a website, including all standard layout elements, from header to the footer, including menus and special boxes. You will learn how to prepare the templates, store them and export them in the form of ready-to-use HTML pages or packages that can be installed in various CMS platforms such as WordPress, Joomla!, Drupal, or DotNetNuke. The last part of the book shows you some tips and tricks that allow you to extend standard themes generated by Artisteer for enriching the website with image gallery, combining two menus, and more.You will learn how to create a professional quality website or CMS template on your own, with the use of Artisteer with minimal technical difficulties.

Elastic Stack 8.x Cookbook. Over 80 recipes to perform ingestion, search, visualization, and monitoring for actionable insights

Huage Chen, Yazid Akadiri, Shay Banon

Learn how to make the most of the Elastic Stack (ELK Stack) products—including Elasticsearch, Kibana, Elastic Agent, and Logstash—to take data reliably and securely from any source, in any format, and then search, analyze, and visualize it in real-time. This cookbook takes a practical approach to unlocking the full potential of Elastic Stack through detailed recipes step by step.Starting with installing and ingesting data using Elastic Agent and Beats, this book guides you through data transformation and enrichment with various Elastic components and explores the latest advancements in search applications, including semantic search and Generative AI. You'll then visualize and explore your data and create dashboards using Kibana. As you progress, you'll advance your skills with machine learning for data science, get to grips with natural language processing, and discover the power of vector search. The book covers Elastic Observability use cases for log, infrastructure, and synthetics monitoring, along with essential strategies for securing the Elastic Stack. Finally, you'll gain expertise in Elastic Stack operations to effectively monitor and manage your system.

Oracle ADF 11gR2 Development Beginner's Guide. Oracle ADF is one of the easiest ways to develop rich internet applications. All you need is a little Java to get the most from this book as it takes you step-by-step from installation, to development, to implementation

Vinod Krishnan, Vinod Thatheri Krishnan

Oracle ADF is an end-to-end framework which makes application development simple by providing infrastructure services as well as visual and declarative development right away. Oracle ADF 11gR2 Development Beginner's Guide guides any user with programming skills to be able to quickly learn the options and ways to develop rich Internet applications using ADF 11gR2. Containing all the skills that a new user has to use to build an application in ADF 11gR2, this book is designed in such a way so that it enhances the practical feel of developing applications in ADF 11gR2. Starting with the installation and configuration of Oracle ADF 11g RD we will then work through topics such as working with the Model Layer and Model Data followed by displaying and binding the data. Later we will look at Navigations and Flows within applications as well as their layout, look, and feel. Oracle ADF 11g R2 Development Beginner's Guide will conclude with us looking at the security and deployment of the applications which have been created.

F# for Quantitative Finance. An introductory guide to utilizing F# for quantitative finance leveraging the .NET platform

Johan Astborg

F# is a functional programming language that allows you to write simple code for complex problems. Currently, it is most commonly used in the financial sector. Quantitative finance makes heavy use of mathematics to model various parts of finance in the real world. If you are interested in using F# for your day-to-day work or research in quantitative finance, this book is a must-have.This book will cover everything you need to know about using functional programming for quantitative finance. Using a functional programming language will enable you to concentrate more on the problem itself rather than implementation details. Tutorials and snippets are summarized into an automated trading system throughout the book.This book will introduce you to F#, using Visual Studio, and provide examples with functional programming and finance combined. The book also covers topics such as downloading, visualizing and calculating statistics from data.F# is a first class programming language for the financial domain.

JavaScript Design Patterns. Deliver fast and efficient production-grade JavaScript applications at scale

Hugo Di Francesco

Unlock the potential of JavaScript design patterns, the foundation for development teams seeking structured and reusable solutions to common software development challenges in this guide to improving code maintainability, scalability, and performance. Discover how these patterns equip businesses with cleaner and more maintainable code, promote team collaboration, reduce errors, and save time and costs.This book provides a comprehensive view of design patterns in modern (ES6+) JavaScript with real-world examples of their deployment in professional settings. You’ll start by learning how to use creational, structural, and behavioral design patterns in idiomatic JavaScript, and then shift focus to the architecture and UI patterns. Here, you’ll learn how to apply patterns for libraries such as React and extend them further to general web frontend and micro frontend approaches. The last section of the book introduces and illustrates sets of performance and security patterns, including messaging and events, asset and JavaScript loading strategies, and asynchronous programming performance patterns.Throughout the book, examples featuring React and Next.js, in addition to JavaScript and Web API examples, will help you choose and implement proven design patterns across diverse web ecosystems, transforming the way you approach development.

Implementing and Administering Cisco Solutions: 200-301 CCNA Exam Guide. Begin a successful career in networking with CCNA 200-301 certification

Glen D. Singh

In the dynamic technology landscape, staying on top of the latest technology trends is a must, especially if you want to build a career in network administration. Achieving CCNA 200-301 certification will validate your knowledge of networking concepts, and this book will help you to do just that.This exam guide focuses on the fundamentals to help you gain a high-level understanding of networking, security, IP connectivity, IP services, programmability, and automation. Starting with the functions of various networking components, you’ll discover how they are used to build and improve an enterprise network. You’ll then delve into configuring networking devices using a command-line interface (CLI) to provide network access, services, security, connectivity, and management. The book covers important aspects of network engineering using a variety of hands-on labs and real-world scenarios that will help you gain essential practical skills. As you make progress, this CCNA certification study guide will help you get to grips with the solutions and technologies that you need to implement and administer a broad range of modern networks and IT infrastructures.By the end of this book, you’ll have gained the confidence to pass the Cisco CCNA 200-301 exam on the first attempt and be well-versed in a variety of network administration and security engineering solutions.

Learning NHibernate 4. Explore the full potential of NHibernate to build robust data access code

Suhas H Chatekar, Suhas Hanmantrao Chatekar, Gabriel N. Schenker