EMI, orelectromagnetic interference, and RFI, or radio-frequency interference, are both types of electromagnetic radiation. EMI is emitted by electronic devices and can interfere with the proper functioning of other electronic devices, while RFI is emitted by radio waves and can interfere with radio signals.
EMI and RFI shielding is a process of enclosing electronic devices in a material that absorbs or reflects electromagnetic radiation to protect the devices from interference.
It can prevent everything from minor crackling during broadcasting to deadly malfunctions in aircraft safety equipment. If left unmitigated, it can disrupt the essential functions of electronic devices or erase or damage data. Even satellites in space need to be shielded from EMI/FRI to function properly.
Common sources of EMI/RFI include cell phones, microwaves, power lines and computer circuits. There are all natural causes of these signals such as auroras, solar flares or lightning.
What is EMI / RFI shielding, and what does it do?
EMI/RFI shielding is a process or material used to protect electronic equipment from EMI and RFI. EMI/RFI shielding can protect against various sources, including radio waves, microwaves, and electrical currents.
EMI/RFI shielding creates a barrier between the electronic equipment and the source of interference. This barrier can be made with a variety of materials.
Materials used for EMI/RFI shielding
For EMI/RFI shielding, avariety of materials can be employed. The following are the most frequent materials:
Metals are the most common material used for EMI/RFI shielding. They are effective because they reflect and absorb electromagnetic radiation.
Importance of EMI / RFI shielding in electronic devices
EMI/RFI shielding is essential in electronic devices because it can help to reduce or eliminate interference that can lead to errors, data loss, and equipment damage. Shielding can also help improve electronic device performance by reducing interference from outside sources.
EMI/RFI shielding creates a barrier between the electronic equipment and the source of interference. This barrier is produced with various materials, including metals, conductive plastics, and special coatings.
How to choose the right EMI / RFI shielding for your needs
When choosing EMI/RFI shielding for your electronic devices, it is vital to consider the type of interference you are trying to protect against, the level of protection you need, and the environment in which the electronic devices will be used.
Some EMI/RFI shielding types, such as metal shielding, can block a wide range of frequencies. However, metal shielding can also block signals you may want to receive, such as radio waves. In addition, metal shielding can interfere with the proper functioning of some electronic devices.
Other EMI/RFI shielding types, such as conductive plastics and special coatings, can be customized to block specific frequencies while allowing others to pass through. These materials can also be used in various environments, including wet or humid ones.
Common applications for EMI / RFI shielding
EMI/RFI shielding is used in a variety of industries, including:
Mass transit systems
Navigation and vehicular control systems
Keep your electronics interference-free
If you’re looking for ways to protect your electronic devices from interference, look no further than EMI and RFI shielding. Enclosed devices in a material designed to absorb or reflect electromagnetic radiation to keep them functioning correctly. At A&J we use a .140 diameter tubular gasket (210-1130) that is added to the extrusion grooves and consists of a silicone inner core that is plated with silver / aluminum for the seams between the frame members that are joined together.
Our enclosures are attenuated to 60 DB from 150 Hz to 1 million Hz and 40 DB from 1-2 million Hz in accordance with MIL-STD-461G for EMI/RFI shielding. Our team of professionals can help you determine the type of shielding your rack or enclosure needs and install it quickly and efficiently.Contact us today!
A rack mount is a description of a hardware device capable of being mounted in an equipment rack. All types of electronics and computing devices come in rack-mounted packages including servers, test instruments, telecommunications components, which are bolted to the side frames of the rack. Note: shelves are available for equipment that is not rack mounted.
Measuring cabinet dimensions, specifically depth
Before ultimately choosing a rack mounting option, let’s first review how to properly measure your rack space. As a reminder, cabinets or enclosures are traditionally referred to by their external dimensions. But in most cases, the rack depth is 4 to 6 inches less than the external cabinet depth.
To measure the rack depth, measure the distance between the forward-most part of the front rail to the rear-most point of the rear rail. A&J typically recommends 34 in. (86.36 cm) or greater cabinets for use with equipment that have an average depth of 28 in. (71.12 cm). The 6 inches (15.24 cm) at the back between the equipment and the back door or panel allows for cable management, airflow and maintenance access.
Equipment mounting options
Originally mounting holes were tapped with a particular screw thread, but has since become problematic where equipment is frequently changed because the threads are easily damaged or the mounting screws can break off. Both problems render the mounting hole unusable.
Tapped-holes were then replaced by clearance-hole racks. Holes are large enough to permit a bolt without binding and fastened in place using cage nuts.
The third innovation has been square-hole racks. These racks allow boltless mounting where the weight of the equipment and small retention clips are all that is necessary to hold equipment in place.
The structural support
A key structural weakness of front-mounted support is the bending stress placed on the both the rack itself and the mounting brackets of the equipment. Our A&J racks can incorporate front and rear rails that may be moved forwards and backwards that allows equipment to be supported by four posts, but also easily installed and/or removed.
Our standard AJR 150 Series 4-post racks are 22.31″ (566.6 mm) wide with three depths: 26″, 30″, 36″ (660.4 mm to 914.4 mm). The extra width and depth enables cabling to be routed with ease and deeper equipment to be installed. It can also accommodate “Zero-U” accessories such as PDUs and vertical cable managers in the space between the rear rails and the side of the enclosure.
Often used for heavy equipment that requires regular servicing, a pair of rails can be mounted directly onto the rack which allows the component to slide into the rack along the rails. The equipment can then be bolted to the rack (as described above) or the rails may also be able to fully support the equipment in a position where it has been slid clear of the rack. Consider purchasing a cable management arm, which folds the cables attached to the server or component and allows them to expand neatly when the rail is slid out, without being disconnected.
You will need some of the following tools to rackmount your equipment:
Philips No. 1, No. 2, and No. 3 screwdrivers
Flat-blade No. 1 and No. 2 screwdrivers
Allen and adjustable wrenches
Electrostatic discharge (ESD) wrist strap
Rack Mounting Tips & Guidelines
Install the heaviest equipment and storage devices in the lowest position in the rack to prevent the rack from becoming too-heavy and prone to tipping over.
Install any remaining equipment from the lowest system upward into the rack.
For applications that require high-density cabling, you may need 1U of horizontal cable management for every 1U of patch panels or switches.
Ensure the rack is properly secured to the floor or ceiling and level before installing any components.
Because the Industrial Internet of Things (IIOT) has accelerated the evolution of industrial engineering, it’s generally a good idea to err on the side of versatility. But there are several misconceptions or misunderstandings about the traits and attributes of a modular enclosure. A fully realized modular enclosure will help you respond better to market demands, supply chain logistics and other variant-rich environments with greater flexibility, agility and speed.
What a Modular Enclosure Is and Isn’t
There are specifically three terms that are used incorrectly.
Unibody Enclosure – Often constructed with welded steel or other heavy sheet metal, their rigid design can hamper maintenance, repair or modification of the enclosure and the equipment within it.
Modified Enclosure – While a modified enclosure can have some of the same traits as a modular enclosure, it simply encompasses an enclosure with custom holes or tapping
Modular Enclosure – an industrial enclosure with accessories or panels that can easily be reconfigured or rearranged within its standard frame. It virtually eliminates costly machining and fabrication as your device components change.
Benefits of a Modular Enclosure
Infinite configurations – Modular frames come with pre-drilled holes using the EIA’s standardized unit of measurement. And common accessories or network devices can be added to the interior without additional drilling or welding. Plus, these frames can easily be bayed together to create nearly infinite configurations.
Faster mounting & installation – Using rails, an integrator can easily slide panels into or out of the front, side or rear openings of an enclosure. Mounting becomes easier and faster when compared to the unibody technique of laying an enclosure on its back and lifting the panel with a forklift or crane. This all adds up to saving you time and money.
Built to last – Due to its vertical framing, a modular cabinet won’t lose any of its strength or protective qualities.
Flexibility – A designer, integrator, engineer and end user each have the freedom to make assemblies as basic or as complex as a job requires. Again, components can be arranged without the need to cut or weld. This allows for varied and unique configurations inside, while also allowing flexible cable or maintenance entry. Any enclosure can be adapted to meet your needs.
Maximizes floor space – Space is a premium and all floor designers / engineers want to maximize the square-footage at their disposal. Modular enclosures can be customized or tailored to fit specific applications in a variety of environments. They unlock efficiencies and flexibility though both inner and outer mounting levels, multiple baying opportunities and accommodate a variety of connection configurations.
Core Elements of a Modular Enclosure
The prime characteristics of a modular enclosure include:
Protection of enclosed devices / equipment – There are several physical stressors present in any given environment: tampering, water, mold, corrosion. And just like traditional unibody designs, a modular enclosure can be certified to rugged industry standards (MIL-S-901D, NEMA). Properly assess local weather conditions, corrosive substances and even resistance levels of internal components.
Compartmentalization – A modular design allows you to compartmentalize separate pieces of IT equipment or add thermal accessories to help with climate control. It removes the need to source several cabinets or climate-control systems. It also saves floor space!
Ease of modification – It’s easier to scale up or scale down manufacturing needs based on production sequence, customer demand, space or other factors with a modular design. And users can easily swap parts out for new ones and modify panels.
Mounting panels – The most commonly modified part of any enclosure, the mounting panel in a modular design allows for the addition of rails, making it possible to slide the panel into and out of the front, side or rear openings. It eliminates the need to lay the enclosure on its back and lifting the panel with a crane or forklift.
Availability of sizes and types – While available in traditional sizes, it can also be configured to specific applications with full size or partial doors, multiple mounting panels and entry points.
Racks help organize IT equipment into more collective assemblies that free up space and make efficient use of resources. A rack typically consists of two or four vertical rails for mounting, along with a supporting framework that secures the rails. Both the framework and rails tend to feature aluminum or steel construction, which makes them capable of supporting up to thousands of pounds of IT equipment. The rails also include round or square holes that make it easy to use screws for mounting rack equipment.
If standard rack designs don’t work for your application, you may benefit from a custom server rack. When creating your custom rack design, there are many key factors to consider to ensure the best possible rack for your needs.
Things to Consider with Custom Racks & Enclosures
When in the market for a custom electronic rack, there are certain items to consider to inform your design.
One element that will go into a custom rack design is the desired size. Obviously all of your electronic components need to fit comfortably inside, but you also need to consider the space between them to avoid interference. Your rack or enclosure should also accommodate the necessary space needed for maintenance and device assembly or installation.
Regarding external size dimensions, the primary limitation is that the bend radius must not be less than the enclosure material’s thickness. Through CNC machining, we can manufacture enclosures as small as 11.75″ x 16.5″ x 9.5″. We encourage you to contact us about your design to discuss it further with our design engineering team.
Depending on the application, you’ll need to account for any industry standards or ratings that enclosures must meet to protect equipment from dust or water. For instance, equipment may need to meet NEMA and military standards or have an IP rating.
Shelves & Drawers — Sliding and fixed shelves and sliding drawers
Shock, Vibration, and Seismic Resistance — Open-frame racks and enclosure racks
Secure Racks — Blanking panels
Standard Options vs. Custom Design
Oftentimes, you may not need a custom rack cabinet if you can benefit from using standard equipment, which is why this is one of the first determinations to make. Customers may also be able to fit a stock enclosure with various custom features instead of designing an entire custom rack, saving more time and resources.
A&J’s racks are modular, which makes them easy to adapt to various hardware and technology.
Other factors to consider include:
Expandability. At A&J, our kits allow us to gang cabinets together to form a “suite,” which helps increase stability and enables easier management of interconnecting cables.
Accessibility. Our cabinets’ bolted-together design makes it easy to remove side panels from the exterior, allowing easy access to interior cabling and components.
Cable Management. Most equipment on a rack requires cabling for operational or network connectivity purposes. Our cable management accessories offer a key solution in these situations.
Lower Upfront Costs
Although you can create custom enclosures in-house, it can be very costly to invest in the required equipment, manufacturing tools, and materials. This equipment can take up a lot of space in your facility and may require lots of trial and error to produce an effective enclosure. Our expertise at A&J can help you avoid these challenges, saving you time and money.
Greater Process Knowledge
Our engineers possess the necessary techniques and expertise to drill into aluminum rack materials without causing any damage.
Lower Labor Costs
When creating custom racks in-house, your staff may have less time to focus on primary goals. It will also make employees work beyond their expertise, leading to reduced productivity. A&J will help reduce labor costs by enabling your staff to spend more time on the tasks they can effectively handle.
Customizing Your Enclosure with A&J
At A&J, we offer custom CNC machining to manufacture custom electronic racks. This allows for precise cuts, reduced scrap, and advanced capabilities. In addition, you’ll benefit from engineering support as well as a wide selection of standard rack sizes and models with accessories that we can easily modify to suit different applications.
To order a custom or standard rack, you can take the following steps:
Browse our selection of standard rack enclosures and accessories to locate the ideal choice
Submit a quote with basic specifications
Upload a drawing, ideally a CAD drawing, for our engineering team to review, or we can draft an initial design with the help of our design engineering services
Place your order, and we’ll ship your rack to the designated final destination
Today, virtually all businesses rely heavily on technology to satisfy their customers, regardless of size. And with these technological advances, we’re starting to place electrical equipment in a variety of nontraditional environments. To ensure proper protection of electrical components, choosing the right electrical enclosure for the application at hand is critical. But first, let’s break down the basic components of an electronic rack.
The Structure of an Electronic Enclosure
Generally tall and rectangular in shape, an enclosure is typically made up of a two- or four-post rack mainframe and mounting rails. Depending on the design, some enclosures have rear and/or front doors, side panels, top panels and bases. Enclosures are highly customizable and various components or areas of the rack can be modified to fit a customer’s needs or environment. If you’ve never seen one outside of a data center or other industrial function, they could easily be mistaken for an extra large filing cabinet.
The terms cabinet and rack are often used interchangeably; however, that would be incorrect. As described above, racks are simply the frame inside a cabinet that is used for mounting all of the electronic equipment. Cabinets enclose a rack and include all of the necessary connections for electrical power, cooling fans for thermal management, and EMI / RFI shielding capabilities. Cabinets themselves come in a wide variety of sizes and colors.
Again, because the two terms are often used conversely, there’s often confusion about how to measure dimensions properly. Cabinets are traditionally measured by their external dimensions while racks are measured from the most-forward portion of the front rail to the rear-most point of the rear rail. We typically recommend at least 6 inches between components and the rear cabinet door to accommodate cable management, airflow and necessary service access to components.
Rack widths are specified by EIA 310D standards and include 19″, 23″, 24″ and 30″ inches. With racks you also need to be mindful of your vertical spacing for all equipment that you plan to mount in your enclosure. EIA 310D-compliant define one rack unit (RU) as 1.75 inches with three mounting holes spaced at 5/8, 5/8 and 1/2 an inch apart.
Equipment Found in a Rack
The design of a rack is rather basic, but the vital equipment inside can process or store an immense amount of information. And military systems specifically often represent extreme environments for COTS electronic equipment. Typically, equipment found in racks support IT or datacomm equipment such as: servers, network switches, GPS and navigation systems and telecommunication routers/hardware. However, there are several industrial applications for cabinets and enclosures too: large-scale battery storage, test system components, and manufacturing or plant floor enclosures.
Equipment layout, whether isolation is required and how the electronics are mounted/”housed”, can vary widely. Racks also accommodate all the accessories that support the equipment itself like PDUs, cable management, patch panels, shelves and drawers, and thermal management systems.
When you’re able to demystify the necessary components and even the basic structure of an electronic enclosure rack, you can more easily identify the features you need. For more information on the products we offer, please contact A&J Manufacturing today or browse our Frequently Asked Questions.
Among some of the most frequently forgotten, yet necessary components of any rack solution are cable managers. Cables are often difficult to incorporate into 3D CAD drawings and since they’re “out of sight, out of mind”, the accessories needed to organize them are also forgotten. But nearly every piece of equipment in your rack requires data cables to provide network connectivity, or at the very least, power cables to make them operable.
Top Cable Management Accessories for your Electronic Rack
With an open-frame rack, we typically recommend vertical cable managers that span the full height of the rack, but they aren’t as commonly used in cabinets or racks with side panels. Instead, consider using vertical cable rings to keep cables organized and prevent them from blocking access to your electronic equipment. To minimize electromagnetic interference (EMI), our design engineers recommend running the rings down the rear rails with all cable powers being routed through the rings on one side and data cables running down the opposite length.
If your rack will house any high-port equipment, the ideal solution is to position horizontal cable managers both above and below the equipment to improve access to both rows of cables and reduce the potential for accidental disconnects.
And even if you don’t use any specific cable management accessories, basic hook and loop cable ties are fundamental to organization. We don’t recommend using zip ties since they will eventually need to be cut and could compromise the cables themselves risking damage and causing waste.
One of the most critical considerations to keep in mind when choosing the appropriate cable management solution for your cabinet is the impact they can have on rail depth. A&J offers three standard rack depths: 19″, 24″ and 30″, but we can also create any custom depth required. Without enough clearance space, the mass of wiring can obstruct airflow and/or the rear panel.
Tips to Make Cable Management Easier
Measure connection distance between components so you’re not wasting money or space on excess cables. Most electronics vendors offer a variety of power cord options or you can purchase your own low-profile power cords to free up additional space.
Proper, well-planned cable markings will simplify any troubleshooting and changes without unnecessary work within the rack. And if you color code your cables this will help differentiate different types of cables. We also recommend labeling both ends so you know exactly where they go and what they’re being used for.
Cable management arms neaten up a rack, but you might also need to consider reducing the server count in a rack to free up space or design a deeper model for adequate clearance.
Carefully plan and execute the cable trunk to avoid obstructions to ventilation and cooling airflow. The last thing you want is running it along a series of servers directly behind their exhaust fans.
ALWAYS confirm how the rack’s overall dimensions fit within your existing floor plan to avoid disruptions to aisle containment or waste IT staff time during setup in a tightly configured layout.
Just like electronic equipment rack designs and accessories, the end use for your product determines the best type of metal finishing option to use for your custom electronic enclosure or rack. Finishes provide a durable coating that protects a product from its environment and function best. Does your enclosure need to be able to withstand high temperatures? Avoid corrosion? Promote electrical conductivity?
Frankly, cost and production time are less important factors. You want the best results possible! Read on to determine which metal finishing option is best for your electronic enclosure.
Metal Finishing Option: Bare Metal Finishes
There are three options: “no finish”, “grained finish” and “tumbled”.
About “No Finish/Natural”
Parts are de-burred with no additional finishing, but minor surface scratches and blemishes are to be expected. There’s no additional cost and best used for functional parts that won’t be on display.
About “Grained Finish”
Parts are de-burred, and then given a specific linear grain direction via brushing. It can only be applied to accessible flat exterior faces on machined parts and can also be digitally printed or silkscreened.
About “Tumbled Finish”
A great option for machined parts, but maximum size is 10x10x10. This process smooths and imparts non-directional finish via tumbling in abrasive medium. It can also be digitally printed or silkscreened.
Metal Finishing Option: Powder Coating
Powder coating is a dry finishing process in which free-flowing, thermoplastic or thermoset powder material, rather than a liquid suspension, is applied to a surface, melted, and then allowed to dry and harden into a protective coating. It provides a better, more durable finish than paint. It’s also highly effective in removing surface defects.
Thicker and specialty finishes available
Less environmental impact
Shorter curing, processing and drying times
Undamaged and uncontaminated powder overspray can be reclaimed and recycled for future applications (utilization rate is close to 100%)
Range of suitable materials is limited due to the fact that it must be heated to be cured
Difficultly producing thin coatings
Not cost-effective for custom, small batch coating needs
Curing and drying times increase for large, heavier parts (due to higher temperatures required)
Metal Finishing Option: Chemical Conversion Coating
Also known as Chem Film or chromate coating, this process applies chromate to a metal surface that is corrosion resistant, durable and exhibits stable electrical conductivity.
If you’re using your rack in a rugged environment, use a vendor that is MIL-DTL-5541F qualified. The standards include utilizing a process that doesn’t use toxic hexavalent chrome and has been replaced with the safer zirconium, titanium or trivalent chromium. It’s also been sufficiently tested against corrosion and proves to have reliable electrical conductivity.
Extends the service life of parts
Cost efficient and economical
Doesn’t change part dimensions
High energy demand
Metal Finishing Option: Anodizing
Anodizing is an electrochemical process that involves dipping aluminum into a bath of acid and passing an electric current through the medium. It converts the surface into a decorative, durable, corrosion-resistant oxide finish.
Anodized aluminum protects satellites from the harsh environment of space, and revolutionized the construction of computer hardware, scientific instruments and consumer products like kitchen appliances.
Durability – creates an extremely hard surface that is more resistant to scratches
Resistant to corrosion, heat and electricity
Low environmental impact – non-toxic finish with no harmful by-products
Limited color selection and its often subject to color variations
Requires a high-grade alloy of aluminum
Not cost effective for small quantities
Contact us today to learn more about the different types and colors of enclosures finishes that are available.
Vibration is bad for electronics. It can damage the boards and components potentially causing permanent failure. But a well-engineered enclosure protects delicate equipment from vibration damage by isolating it from external sources. Utilizing a stabilizer kit for your rack can add an additional layer of security.
These vital electronics are subjected to stressors in a wide spectrum of applications ranging from in-office or industrial power stations to ruggedized, aerospace systems or other military deployment. Even if intended for more mild environments, nearly all electronics are subject to some level of vibration during their lifecycle. Typical shock values for industrial use might be in the 5G to 10G range whereas systems on naval ships need to withstand shocks in excess of 20G.
If your equipment is mounted on a ground-based or airborne vehicle, shipboard mounted or needs to withstand natural weather patterns and seismic events, ruggedized construction should be one of the, if not THE, primary design criteria.
There are two types of vibration: random or sinusoidal. Random is a varying waveform similar to riding in a vehicle rolling across rough terrain. Sinusoidal vibration occurs at distinct frequencies and is continuous, like that of a rotating engine on a helicopter.
Stress testing can uncover defects in a design before they become expensive problems. And often times, the only way to verify that a rack and its isolation mounts will provide sufficient protection is through instrumented testing. Our A&J electronic equipment racks have been designed and tested to meet MIL standards:
MIL-S-901C Blows Total weight 845 lbs. Hard mounted
Shock and Vibration
MIL-STD-810, method 516 Isolation system installed Vibration to 33 Hz
72 H, 30 D
MIL-S-901C Total weight 638 lbs. Vibration to 33 Hz
MIL-S-901C 9 Total weight 1254 lbs. Hard mounted
Shock and Vibration
MIL-S-901C 9 Blows Total weight 1254 lbs. Isolation system installed
Shock and Vibration
MIL-S-901C 12 Blows Total weight 998 lbs. Hard mounted Vibration to 33 Hz
Shock and Vibration
MIL-S-901C 9 Blows Total weight 865 lbs. Hard mounted Simulated weight
Shock and vibration
MIL-S-901C 9 Blows Two racks joined at the top Total weight 1262 lbs. Hard mounted
Shock and vibration
MIL-S-901C 6 Blows Total weight 450 lbs. High temp & humidity
Shock and vibration
72 H, 36 D, 36 W
MIL-S-901C 9 Blows Total weight 695 lbs. Internal isolation systems
MIL-S-901C 9 Blows Total weight 650 lbs. Hard mounted
Shock and Vibration
MIL-S-901C Blows Total weight 922 lbs. Free standing
Shock and vibration
MIL-S-901C 9 Blows Total weight 928 lbs. Hard mounted Simulated weight
Key rack components to protect against shock & vibration
The main goal in handling shock and vibration is to isolate the equipment from excitement by reducing the amplitude and frequency of waves. Enter: isolators. They’re critical! And act as a highly stable buffer between the source of the vibration and the object or surface. A good system has two main components, a spring to support the load and a damping element to dissipate the energy.
Two common types of vibration isolators are used in rack configurations:
Wire Rope Coils – the ideal solution for providing low frequency, highly damped vibration isolation and excellent shock attenuation. They often require little maintenance, are made from durable metals and keep functioning under varying temperatures in corrosive environments.
Seismic Mounts – whether you’re in a seismic region of the country or on a Naval ship, these mounts are designed to provide the strength and isolation necessary to control the motion of equipment
Varying the size, shape, construction material and number of coils all affect the spring rate and damping, as well as mounting placement.
Common applications for vibration and shock isolators include avionics and equipment, computer equipment and disc drivers, control panels, electrical transformers, fans and blowers, industrial machinery, marine and shipboard equipment, medical equipment, power plants and cooling towers, pumps and centrifuges, and compressors.
Obviously, the rack’s exterior frame should be rigid construction to withstand any buckling. At A&J, we developed a unique bolted-together design that lends structural integrity, eliminating the need for welding. The modular design allows a wide range of sizes and configurations to be incorporated. For seismic zones or rugged applications, a back stiffener or X-brace can be added near the top, middle and bottom to protect from movement. Another option to consider is double-walled construction where the frame has two layers of sheet metal for extra strength.