Deep Freeze Standard Edition 7.51.020.4170 Incl. License 61
Toccara Delacerda
The Object.freeze() static method freezes an object. Freezing an object prevents extensions and makes existing properties non-writable and non-configurable. A frozen object can no longer be changed: new properties cannot be added, existing properties cannot be removed, their enumerability, configurability, writability, or value cannot be changed, and the object's prototype cannot be re-assigned. freeze() returns the same object that was passed in.
Private properties do not have the concept of property descriptors. Freezing an object with private properties does not prevent the values of these private properties from being changed. (Freezing objects is usually meant as a security measure against external code, but external code cannot access private properties anyway.) Private properties cannot be added or removed from the object, whether the object is frozen or not.
Note that as the standard three properties (buf.byteLength, buf.byteOffset and buf.buffer) are read-only (as are those of an ArrayBuffer or SharedArrayBuffer), there is no reason for attempting to freeze these properties.
To be a constant object, the entire reference graph (direct and indirect references to other objects) must reference only immutable frozen objects. The object being frozen is said to be immutable because the entire object state (values and references to other objects) within the whole object is fixed. Note that strings, numbers, and booleans are always immutable and that Functions and Arrays are objects.
The result of calling Object.freeze(object) only applies to the immediate properties of object itself and will prevent future property addition, removal or value re-assignment operations only on object. If the value of those properties are objects themselves, those objects are not frozen and may be the target of property addition, removal or value re-assignment operations.
To make an object immutable, recursively freeze each non-primitive property (deep freeze). Use the pattern on a case-by-case basis based on your design when you know the object contains no cycles in the reference graph, otherwise an endless loop will be triggered. An enhancement to deepFreeze() would be to have an internal function that receives a path (e.g. an Array) argument so you can suppress calling deepFreeze() recursively when an object is in the process of being made immutable. You still run a risk of freezing an object that shouldn't be frozen, such as window.
\n Note that as the standard three properties (buf.byteLength,\n buf.byteOffset and buf.buffer) are read-only (as are those of\n an ArrayBuffer or SharedArrayBuffer), there is no reason for\n attempting to freeze these properties.\n
\n To be a constant object, the entire reference graph (direct and indirect references to\n other objects) must reference only immutable frozen objects. The object being frozen is\n said to be immutable because the entire object state (values and references to\n other objects) within the whole object is fixed. Note that strings, numbers, and\n booleans are always immutable and that Functions and Arrays are objects.\n
\n The result of calling Object.freeze(object) only applies to the\n immediate properties of object itself and will prevent future property\n addition, removal or value re-assignment operations only on\n object. If the value of those properties are objects themselves, those\n objects are not frozen and may be the target of property addition, removal or value\n re-assignment operations.\n
\n To make an object immutable, recursively freeze each non-primitive property\n (deep freeze). Use the pattern on a case-by-case basis based on your design when you\n know the object contains no cycles in the reference\n graph, otherwise an endless loop will be triggered. An enhancement to\n deepFreeze() would be to have an internal function that receives a path\n (e.g. an Array) argument so you can suppress calling deepFreeze()\n recursively when an object is in the process of being made immutable. You still run a\n risk of freezing an object that shouldn't be frozen, such as window.\n
Cryosurgery has been used to treat skin lesions for approximately 100 years. The first cryogens were liquid air1 and compressed carbon dioxide snow.2 Liquid nitrogen became available in the 1940s and currently is the most widely used cryogen.
Over the past 50 years, much experience has been gained in the use of cryosurgery to treat skin lesions.3 The cotton-tipped dipstick method of liquid nitrogen application has been popular in the management of common benign lesions (Figure 1, left). However, this method is being supplanted by liquid nitrogen spray techniques (Figure 1, center). Liquid nitrogen spray equipment (Figure 2) is easy to use, and similar techniques can be employed to manage benign, premalignant, and malignant lesions.
Irreversible damage in treated tissue occurs because of intracellular ice formation. The degree of damage depends on the rate of cooling and the minimum temperature achieved. Inflammation develops during the 24 hours after treatment, further contributing to destruction of the lesion through immunologically mediated mechanisms.
Slow thaw times and repeat freeze-thaw cycles produce more tissue injury than a single freeze and thaw. Usually, several minutes are allowed between repeat freeze-thaw cycles. Repeat freeze-thaw cycles generally are employed only in the treatment of malignancy.
Continuous freezing at one location for more than 30 seconds beyond when an adequate freeze ball is achieved around the target area can result in disruption of the collagen matrix of the skin and possible scarring.
Mild freezing leads to dermoepidermal separation, which is useful in treating benign epidermal lesions. The more sensitive cells in the epidermis are destroyed while the dermis is left intact. Treatment may be complicated by an element of hypopigmentation, but studies and clinical experience indicate that repigmentation often occurs over several months because of undamaged melanocytes within hair follicles or the migration of melanocytes from the edge of the frozen zone.4 However, the predictability of repigmentation in individual patients is uncertain.
The dose of liquid nitrogen and the choice of delivery method depend on the size, tissue type, and depth of the lesion. The area of the body on which the lesion is located and the required depth of freeze also should be considered. Additional patient factors to consider include the thickness of the epidermis and underlying structures, the water content of the skin, and local blood flow.
The timed spot freeze technique allows greater standardization of liquid nitrogen delivery. It may be the most appropriate method for physicians who are learning to perform cryosurgery. Use of this technique maximizes the ability to destroy a lesion with minimal morbidity. The freezing time is adjusted according to variables such as skin thickness, vascularity, tissue type, and lesion characteristics.
Timed spot freezing is performed with a small spray gun that typically holds 300 to 500 mL of liquid nitrogen. Nozzle sizes range from A through F, with F representing the smallest aperture. Nozzle sizes B and C are suitable for the treatment of most benign and malignant lesions; they are the apertures most frequently noted in case reports.
For the standard spot freeze technique, the nozzle of the spray gun is positioned 1 to 1.5 cm from the skin surface and aimed at the center of the target lesion (Figure 4). The spray gun trigger is depressed, and liquid nitrogen is sprayed until an ice field (or ice ball) encompasses the lesion and the desired margin (Figure 5). The designated ice field may need to be delineated in advance with a skin marker pen, because freezing may blur pretreatment lesion margins.
Once the ice field has filled the specified margin, the spray needs to be maintained, with the spray canister trigger pressure and, thus, the liquid nitrogen spray flow adjusted to keep the target field frozen for an adequate time. This time may vary from five to 30 seconds beyond the initial time for formation of the ice field. If more than one freeze-thaw cycle is required for lesion destruction, complete thawing should be allowed before the next cycle (usually two to three minutes).
The timed spot freeze technique achieves temperatures that are adequate for tissue destruction in an ice field up to 2 cm in diameter. The best approach for lesions larger than 2 cm (including an adequate margin) is to use overlapping treatment fields. A detailed discussion of this approach is beyond the scope of this article.
Variations on the open spray technique include the rotary or spiral pattern and the paintbrush method. These techniques can be useful for treating larger benign lesions. They are not well standardized for ensuring the temperatures that are required for the destruction of malignant lesions.5,6
While the open spray technique can be used for the most easily accessible lesions, a cryoprobe (Figure 1, right) attached to the liquid nitrogen spray gun can provide added versatility, depending on the site and type of the lesion. Various sizes and types of cryoprobes are available (Figure 6). The cryoprobe is applied directly to the lesions. A gel interface medium often is used between the probe and the skin surface.
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