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                                                                 EXHIBIT 10.2

                                   REVOLVING
                                COMMERCIAL NOTE

                               IMPORTANT NOTICE
                               ----------------

THIS INSTRUMENT CONTAINS A CONFESSION OF JUDGMENT PROVISION WHICH CONSTITUTES A
WAIVER OF IMPORTANT RIGHTS YOU MAY HAVE AS A DEBTOR AND ALLOWS THE CREDITOR TO
           OBTAIN A JUDGMENT AGAINST YOU WITHOUT ANY FURTHER NOTICE.

$1,500,000.00                                      October 31, 2000

          FOR VALUE RECEIVED, the undersigned (the "Borrower") jointly and
severally promise to pay to the order of UNITED BANK (the "Bank," which term
shall include any holder of this Note) without offset, on November 30, 2001 (the
"Date of Maturity") at the Bank's office located at 2071 Chain Bridge Road,
Vienna, Virginia 22182 (or at such other address as the Bank shall designate),
the principal sum of One Million Five Hundred Thousand and no/100 Dollars
($1,500,000.00) (hereinafter called "Principal Sum"), or so much of that sum as
the Bank may advance, together with interest on the principal balance
outstanding from time to time at the rate provided in this Note.

          INTEREST RATE. This Note shall bear interest on the principal balance
outstanding from time to time, from the date of this Note until paid in full, a
variable rate per annum equal, at all times, to the Prime Rate plus 1.0%. The
"Prime Rate" shall mean that variable rate of interest published in The Wall
Street Journal from time to time as the domestic prime rate under the heading
"Money Rates". Adjustments to a variable interest rate will be effective,
without prior notice, as of the effective date of any change in the Prime Rate.
Interest shall be computed on the basis of a 360 day year, counting the actual
number of days elapsed. If The Wall Street Journal shall cease to publish the
Prime Rate, the term "Prime Rate" shall thereafter mean the rate announced from
time to time by the Bank as its prime rate of interest and evidenced by a
certificate signed by any officer of the Bank setting forth said prime rate of
interest in effect on any given date, whether or not such rate is otherwise
published or announced.

          PAYMENT OF INTEREST. The Borrower agrees to pay accrued interest
beginning November 30, 2000, and on the last day of each consecutive month
thereafter until this Note is paid in full.

          PREPAYMENT. The Borrower may pay the whole or any part of the
outstanding indebtedness evidenced by this Note at any time without penalty by
paying the principal amount to be prepaid together with accrued interest thereon
to the date of prepayment.

          ADVANCES. The Borrower may borrow at any time and from time to time
from the date hereof to the Date of Maturity, such amounts as the Borrower may
request, subject to the provisions hereof and of the Loan Agreement.

                                  Page 1 of 7
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          DEFAULT.  Each of the following events or conditions shall constitute
a default ("Default") under this Note:

          (a)   the failure to make any payment of principal, interest or any
other amount due under this Note when such payment is due;

          (b)   any default under the terms of any of the Loan Documents, or the
failure to perform or observe any warranty, covenant, or other condition of any
of the Loan Documents;

          (c)   any default by the Borrower or any indorser or guarantor of the
payment of this Note with respect to any indebtedness to the Bank (other than
this Note);

          (d)   the death, incompetence, merger, consolidation, reorganization,
dissolution, or termination of existence of any Party; or the pledge, lease or
other disposition, without the prior written approval of the Bank, of all or
substantially all of the assets of any Party;

          (e)   any change, or any transaction which results or could result in
a change, in the Control of any Party;

          (f)   the determination by the Bank that any warranty, representation,
certificate, statement or information provided by any Party or any Person on
behalf of a Party to the Bank in connection with any of the Loan Documents, or
to induce the Bank to make or extend or modify the terms of the loan evidenced
by this Note, was false or misleading, or that any Party or any Person on behalf
of a Party failed to provide or disclose any material facts or information,
which failure rendered such warranty, representation, certificate, statement or
information materially misleading;

          (g)   the inability of any Party to pay its debts as they mature, the
insolvency of any Party, the filing of a petition by or against any Party under
the provisions of any bankruptcy, reorganization, arrangement, insolvency,
liquidation or similar law for relief of debtors, the appointment or application
for appointment of any receiver for any Party or the property of any Party, the
issuance or service of any attachment, levy, garnishment, tax lien or similar
process against any Party or the property of any Party, the entry of a judgment
against any Party, or an assignment for the benefit of creditors by any Party;

          (h)   any agreement or other document granting the Bank security for
the payment of this Note shall cease for any reason to be in full force and
effect as such security with the priority stated to be created thereby, or the
grantor of such security shall contest the validity or enforceability of the
security or deny that it has any further liability or obligation under such
agreement or other document; provided that the Borrower shall have the
opportunity to cure any such cessation in the effect or priority of such
security resulting from any act or omission by the Bank for a period of ten (10)
days after notice thereof from the Bank to the Borrower.

                                  Page 2 of 7
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          (i)  any indorsement or guaranty of the payment of this Note shall
cease for any reason to be in full force and effect, or any indorser or
guarantor shall contest the validity or enforceability of the indorsement or
guaranty or deny that it has any further liability or obligation under the
indorsement or guaranty; or

          (j)  the determination by the Bank that (i) there has occurred a
material adverse change in the financial condition of any Party, (ii) the value
of any property securing this Note has been materially impaired, or (iii) there
has occurred or developed an event or condition which materially impairs the
prospect of payment or performance of any of the obligations of any Party under
the Loan Documents.

          ACCELERATION. At the option of the Bank, upon the occurrence of a
Default as defined above, the full amount remaining unpaid on this Note shall
become immediately due and payable without presentment, demand or notice of any
kind; no additional advances shall be made to the Borrower under this Note; and
the Bank may exercise any or all remedies available to it under applicable law
and the Loan Documents.

          CONFESSION OF JUDGMENT. The Borrower appoints Philip C. Baxa, Esquire,
and Mary C. Zinsner, Esquire, either of whom may act, as its duly constituted
attorney-in-fact with authority, in the name, place, and stead of the Borrower,
to confess judgment in the office of the clerk of the Circuit Court of Fairfax
County, Virginia against it, in the full amount due under this Note, upon the
occurrence of a Default under this Note.

          ACCOUNT RECORD. The Bank shall maintain records of the dates and
amounts of advances of principal and payments of principal and interest, the
date to which interest has been paid, accrued interest, the unpaid principal
balance, and any other account information. Such records shall be maintained
unilaterally by the Bank without notice to the Borrower and shall be presumed to
be correct, provided, however, any failure of the Bank to maintain such records
or any error therein or in any notice hereunder shall not in any manner affect
the obligation of the Borrower to pay this Note in accordance with the terms
hereof.

          IMMEDIATELY AVAILABLE FUNDS. The principal of and interest on this
Note shall be payable in immediately available funds in lawful money of the
United States which shall be legal tender for public and private debts at the
time of payment. The making of any payment in other than immediately available
funds which the Bank, at its option, elects to accept shall be subject to
collection, and interest shall continue to accrue until the funds by which
payment is made are available to the Bank for its use.

          ADJUSTMENT TO BILLING NOTICE. If, because a variable interest rate or
the outstanding principal balance of this Note changes between the date of a
billing notice and the end of a billing period or the Date of Maturity, the
actual amount due and payable is different from the amount billed, then the
amount billed must be paid. The next following billing notice shall be adjusted
by the amount of the difference, or a supplemental billing notice or rebate, as
the case may be, shall be sent to

                                  Page 3 of 7
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the Borrower following the Date of Maturity. A supplemental billing notice
following the Date of Maturity shall be immediately due and payable in full.

          APPLICATION OF PAYMENTS. Payments will be applied to interest, late
charges and other charges due at the time such payments are received, and
principal, in that order. All payments shall be applied to satisfaction of
scheduled payments in the order in which they become due.

          WAIVER. The Borrower and any indorser of this Note (i) waive
presentment, demand, protest and notice of dishonor and protest, (ii) waive the
benefit of their homestead exemptions as to this debt, (iii) waive any right
which they may have to require the Bank to proceed against any other Party or
any collateral given to secure the payment of this Note, and (iv) agree that,
without notice to the Borrower or any indorser and without affecting the
liability of the Borrower or any indorser, the Bank, at any time or times, may
grant extensions of the time for any payment due on this Note or any other
indulgence or forbearance, release any Party from the obligation to make
payments on this Note, permit the renewal of this Note, or permit the
substitution, exchange or release of any security for this Note.

          LATE CHARGE; ATTORNEYS' FEES. If the Borrower fails to pay any amount
due under this Note within 10 days of the date due, the Borrower shall pay to
the Bank on demand a late charge equal to five percent (5%) of the amount due.
The Borrower shall pay to the Bank on demand all costs incurred by the Bank, and
reasonable attorneys' fees, in the collection or enforcement of this Note in the
event of Default, whether or not suit is brought

          SET-OFF. The Bank will have the right upon the occurrence of a
Default, in addition to all other remedies permitted by law (including, without
limitation, other rights of set-off), to set off the amount now or hereafter due
under this Note or due under any other obligation of the Borrower to the Bank
against any and all accounts, credits, money, securities, or other property now
or hereafter on deposit with, held by, or in the possession of the Bank to the
credit or for the account of the Borrower, without notice to or consent by the
Borrower. In addition to the right of set-off, to secure the payment of this
Note the Borrower assigns and grants to the Bank a security interest in all
accounts, credits, money, securities, or other property now or hereafter on
deposit with, held by, or in the possession of the Bank to the credit or for the
account of the Borrower.

          DEFINITIONS. The following terms, as used in this Note, have the
following meanings:

          "Control" of any Person means (i) ownership, control, or power to vote
20% or more of any class of voting securities of such Person, directly or
indirectly or acting through one or more other Persons; (ii) control in any
manner over the election or appointment of a majority of the directors,
trustees, managers or general partners (or individuals exercising similar
functions) of such Person; (iii) the direct or indirect power to exercise a
controlling influence over the management or policies of such Person, whether
through the ownership of voting securities, by contract, or otherwise; or (iv)
conditioning in any manner the transfer of 20% or more of any class of voting
securities of such Person upon the transfer of 20% or more of any class of
voting securities of another Person.

                                  Page 4 of 7
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          "Loan Agreement" means that certain Loan and Security Agreement dated
as of June 29, 1999 between the Borrower and the Bank, and all modifications of,
replacements for, and supplements to, said agreement.

          "Loan Documents" means this Note, the Loan Agreement, the "Term Note"
(as defined in the Loan Agreement) and any other instrument or agreement which
now or hereafter evidences, governs, secures or guaranties the indebtedness
evidenced by this Note, including any loan agreement, deed of trust,
subordination agreement, security agreement or guaranty, and all renewals,
extensions and modifications thereof and substitutions therefor.

          "Party" means the Borrower, any indorser or guarantor of this Note,
any grantor or debtor giving security for this Note, and any other obligor on
any of the Loan Documents.

          "Person" means an individual, a corporation, a partnership, an
association, a limited liability company, a trust or any other entity or
organization.

          ADDITIONAL TERMS.

          The proceeds of this Note shall be used to acquire or carry on a
business, professional, investment, or commercial enterprise or activity.

          The rights and remedies of the Bank under this Note, the other Loan
Documents, and applicable law shall be cumulative and concurrent, and the
exercise of any one or more of them shall not preclude the simultaneous or later
exercise by the Bank of any or all such other rights or remedies. In the event
any provision of this Note is held to be invalid, illegal, or unenforceable for
any reason, then such provision only shall be deemed null and void and shall not
affect any other provisions of this Note, which shall remain effective. No
modification or waiver of any provision of this Note shall be effective unless
it is in writing and signed by the Bank, and any such waiver shall be effective
only in the specific instance and for the specific purpose for which it is
given. The failure of the Bank to exercise its option to accelerate this Note as
provided above, or to exercise any other option, right or remedy, in any one or
more instances, or the acceptance by the Bank of partial payments or partial
performance, shall not constitute a waiver of any Default, or the right to
exercise any option, right or remedy at any time. The nouns, pronouns, and verbs
used in this Note shall be construed as being of such number and gender as the
context may require.

          This Note is a renewal of that certain Revolving Commercial Note dated
June 29, 1999, from the Borrower to the Bank, the obligations under which are
suspended.

          This Note shall be governed by and construed in accordance with the
laws of the Commonwealth of Virginia.

                                  Page 5 of 7
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          WITNESS the following signature and seal:

                                 HADRON, INC.                   [SEAL]
Suite 300
5904 Richmond Highway
Alexandria, Virginia  22303      By: ____________________________________
                                       Name:
                                       Title:

                                 AVENUE TECHNOLOGIES, INC.      [SEAL]
Suite 300
5904 Richmond Highway
Alexandria, Virginia  22303

                                 By: ____________________________________
                                       Name:
                                       Title:

                                 VAIL RESEARCH AND TECHNOLOGY CORPORATION

                                                                [SEAL]
Address:

                                 By: ____________________________________
                                       Name:
                                       Title:

                                 SYCOM SERVICES, INC.           [SEAL]
Address:

                                 By: ____________________________________
                                       Name:
                                       Title:

                                  Page 6 of 7
<PAGE>

                              ENGINEERING & INFORMATION SERVICES, INC.
                                                                        [SEAL]
Address:

                              By: ____________________________________
                                       Name:
                                       Title:

                                Page of 7 of 7<PAGE>

                                                                    EXHIBIT 10.3

                                 JOINDER AGREEMENT

       THIS JOINDER AGREEMENT, effective in all respects as of the 31st day of
October 2000, is by and among ADVANCED BIOSYSTEMS, INC., a Delaware corporation
(the "Co-Borrower"), UNITED BANK, a Virginia banking corporation (the "Bank"),
HADRON, INC., a New York corporation, AVENUE TECHNOLOGIES, INC., a Virginia
corporation, VAIL RESEARCH AND TECHNOLOGY CORPORATION, a Virginia corporation,
SYCOM SERVICES, INC., a Delaware corporation, and ENGINEERING & INFORMATION
SERVICES, INC., a Virginia corporation (collectively, the "Borrower"); and JON
M. STOUT (the "Guarantor").

                                 WITNESSETH THAT:

       WHEREAS, the Bank is the owner and holder of (i) that certain Revolving
Commercial Note dated October 31, 2000, made by the Borrower and payable to the
order of the Bank, in the original principal amount of One Million Five Hundred
Thousand and no/100 Dollars ($1,500,000.00) and bearing interest and being
payable in accordance with the terms and conditions therein set forth (the
"Revolving Note"); and (ii) that certain Commercial Note dated June 29, 1999,
made by the Borrower and payable to the order of the Bank, in the original
principal amount of One Million Five Hundred Thousand and no/100 Dollars
($1,500,000.00) and bearing interest and being payable in accordance with the
terms and conditions therein set forth (the "Term Note") (the Revolving Note and
the Term Note being sometimes referred to herein collectively as the "Notes");
and

       WHEREAS, the Notes are issued pursuant to the terms of a certain Loan and
Security Agreement dated June 29, 1999, between the Borrower and the Bank (as
amended by a certain First Modification and Extension Agreement dated as of
April 12, 2000, a Second Modification Agreement dated as of August 23, 2000, and
a Third Modification and Extension Agreement dated October 31, 2000, the "Loan
Agreement"); and

       WHEREAS, the Co-Borrower has agreed to assume liability for the payment
of, and obligations under, the Loan Agreement, the Notes and the Loan Documents
(as defined in the Notes).

       NOW, THEREFORE, for Ten Dollars ($10.00) and for other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto agree as follows:

       1.   The Co-Borrower hereby assumes and agrees to be jointly and
severally personally liable for payment of each of the Notes and each
installment thereon, and all amounts due under the Loan Agreement, as and when
the same shall become due and payable, whether by acceleration or otherwise, and
for the performance when due of each of the terms, conditions, covenants and
obligations set forth in the Loan Agreement, the Notes and said Loan Documents.

       2.   The parties hereto hereby acknowledge that the outstanding principal
balance of the Revolving Note as of the effective date hereof is
$__________________, and the outstanding principal balance of the Term Note as
of the effective date hereof is $__________________, and that there are no set-
offs or defenses against either of the Notes or the Loan Agreement.
<PAGE>

       3.   Further to induce the Bank to accept this Joinder Agreement, the
Borrower hereby reaffirms the representations and warranties set forth in
Section V of the Loan Agreement and the Co-Borrower hereby makes the
representations and warranties of the Borrower set forth in Section V of the
Loan Agreement as to itself.

       4.   The Guarantor joins in this Joinder Agreement for the purpose of
signifying his consent hereto and acknowledges and agrees that there are no set-
offs or defenses against his guaranty and that his guaranty of the Notes shall
apply to the Notes as modified hereby.

       5.   This Joinder Agreement shall be governed in all respects by the law
of the Commonwealth of Virginia and shall be binding upon and shall inure to the
benefit of the parties hereto and their respective heirs, executors, personal
representatives, successors and assigns.

       WITNESS the following signatures and seals effective as of the day and
year first hereinabove written.

                              HADRON, INC.                   [SEAL]

                              By: ____________________________________
                                    Name:
                                    Title:

                              AVENUE TECHNOLOGIES, INC.      [SEAL]

                              By: ____________________________________
                                    Name:
                                    Title:

                              VAIL RESEARCH AND TECHNOLOGY CORPORATION
                                                             [SEAL]

                              By: ____________________________________
                                    Name:
                                    Title:

                                      -2-
<PAGE>

                              SYCOM SERVICES, INC.           [SEAL]

                              By: ____________________________________
                                    Name:
                                    Title:

                              ENGINEERING & INFORMATION SERVICES, INC.  [SEAL]

                              By: ____________________________________
                                    Name:
                                    Title:

                              ADVANCED BIOSYSTEMS, INC.              [SEAL]

                              By: ____________________________________
                                    Name:
                                    Title:

                              __________________________________     [SEAL]
                              JON M. STOUT

                              UNITED BANK                            [SEAL]

                              By: ____________________________________
                                    Louise M. Wager,
                                    Senior Vice President

                                      -3-

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